cgeo: [Nightly] Syc'ing themes folder to internal storage does not work

Describe the bug: After upgrading to the latest nightly this morning I got the wizard for changing the _themes folder from Legacy to SAF. Did so, everything seemed to run smooth, the wizard sync’ed the folder to internal storage (as he reported in the popup), but after opening the OSM live map, I do not see any themes at all anymore. And there should be plenty of … (about 16 or so, cause currently I experiment with different sizes for texts and symbols and stuff).

To Reproduce: Steps to reproduce the behavior:

1. let the wizard switch your themes folder to SAF notation
2. open live map (default theme is shown)
3. try to switch to a differnet theme …

Actual behavior/state after performing these steps: Apart from default there are no themes at all.

Expected behavior/state after performing these steps: My themes should be there as usual.

Version of c:geo used: 2021.02.24-NB-8f387a6

Is the problem reproducible: Yes

System information:

--- System information ---
c:geo version: 2021.02.24-NB-8f387a6

Device:
-------
- Device type: VOG-L29 (VOG-L29EEA, HUAWEI)
- Android version: 10
- Android build: VOG-L29 10.1.0.150(C431E19R2P5)
- Sailfish OS detected: false
- Google Play services: disabled - 21.02.14 (120400-352619232)
- HW acceleration: enabled (default state)

Sensor and location:
-------
- Low power mode: inactive
- Compass capabilities: yes
- Rotation vector sensor: present
- Orientation sensor: present
- Magnetometer & Accelerometer sensor: present
- Direction sensor used: rotation vector

Program settings:
-------
- Hide caches: own/found archived
- Hide waypoints: -
- Set language: en_DE (system default)
- System date format: dd/MM/y
- Debug mode active: no
- Live map mode: true
- Global filter: display all caches
- Last backup: 23 Feb, 22:49
- Routing mode: Car

Services:
-------
- Geocaching sites enabled:
   geocaching.com: Logged in (Login OK) / PREMIUM
   extremcaching.com: Logged in (Login OK)
- Geocaching.com date format: dd MMM yy
- BRouter connection available: true
- Installed c:geo plugins: contacts

Permissions & paths:
-------
- Fine location permission: granted
- Write external storage permission: granted
- System internal c:geo dir: /data/user/0/cgeo.geocaching (64,9 GB free) v1 internal isDir(6 entries)
- Legacy User storage c:geo dir: /storage/emulated/0/cgeo (64,9 GB free) v1 external non-removable isDir(7 entries)
- Geocache data: /storage/emulated/0/Android/data/cgeo.geocaching/files/GeocacheData (64,9 GB free) v1 external non-removable isDir(238 entries)
- Public Folders: #9
- BASE: /cgeo (User-defined)[/cgeo[DOCUMENT#0:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::], default: /storage/emulated/0/cgeo[FILE#0:p-file:///storage/emulated/0/cgeo::]] (Uri: content://com.android.externalstorage.documents/tree/primary%3Acgeo/document/primary%3Acgeo, Available:true, Files: 56, subdirs:13, free space: 64,9 GB, files on device: 13278715)
- OFFLINE_MAPS: ‎‏‎‎‎‎‎‏‎‏‏‏‎‎‎‎‎‎‏‎‎‏‎‎‎‎‏‏‏‏‏‏‎‏‎‏‏‎‏‏‎‎‎‏‏‏‏‎‏‏‎‎‎‎‎‏‎‎‏‏‎‎‎‎‏‏‏‏‎‏‎‎‎‏‏‏‎‎‏‏‏‎‏‎‏‎‎‏‎‎‏‏‎‎‏‎SD card‎‏‎‎‏‎/Locus/mapsVector (User-defined)[‎‏‎‎‎‎‎‏‎‏‏‏‎‎‎‎‎‎‏‎‎‏‎‎‎‎‏‏‏‏‏‏‎‏‎‏‏‎‏‏‎‎‎‏‏‏‏‎‏‏‎‎‎‎‎‏‎‎‏‏‎‎‎‎‏‏‏‏‎‏‎‎‎‏‏‏‎‎‏‏‏‎‏‎‏‎‎‏‎‎‏‏‎‎‏‎SD card‎‏‎‎‏‎/Locus/mapsVector[DOCUMENT#0:p-content://com.android.externalstorage.documents/tree/0123-4567%3ALocus%2FmapsVector::], default: /cgeo/maps[PERSISTABLE_FOLDER(BASE)#1:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::/maps]] (Uri: content://com.android.externalstorage.documents/tree/0123-4567%3ALocus%2FmapsVector/document/0123-4567%3ALocus%2FmapsVector, Available:true, Files: 1234, subdirs:9, free space: 156,2 GB, files on device: 0)
- OFFLINE_MAP_THEMES: ‎‏‎‎‎‎‎‏‎‏‏‏‎‎‎‎‎‎‏‎‎‏‎‎‎‎‏‏‏‏‏‏‎‏‎‏‏‎‏‏‎‎‎‏‏‏‏‎‏‏‎‎‎‎‎‏‎‎‏‏‎‎‎‎‏‏‏‏‎‏‎‎‎‏‏‏‎‎‏‏‏‎‏‎‏‎‎‏‎‎‏‏‎‎‏‎SD card‎‏‎‎‏‎/Locus/mapsVector/_themes (User-defined)[‎‏‎‎‎‎‎‏‎‏‏‏‎‎‎‎‎‎‏‎‎‏‎‎‎‎‏‏‏‏‏‏‎‏‎‏‏‎‏‏‎‎‎‏‏‏‏‎‏‏‎‎‎‎‎‏‎‎‏‏‎‎‎‎‏‏‏‏‎‏‎‎‎‏‏‏‎‎‏‏‏‎‏‎‏‎‎‏‎‎‏‏‎‎‏‎SD card‎‏‎‎‏‎/Locus/mapsVector/_themes[DOCUMENT#0:p-content://com.android.externalstorage.documents/tree/0123-4567%3ALocus%2FmapsVector%2F_themes::], default: /cgeo/themes[PERSISTABLE_FOLDER(BASE)#1:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::/themes]] (Uri: content://com.android.externalstorage.documents/tree/0123-4567%3ALocus%2FmapsVector%2F_themes/document/0123-4567%3ALocus%2FmapsVector%2F_themes, Available:true, Files: 1215, subdirs:8, free space: 156,2 GB, files on device: 0)
- LOGFILES: /cgeo/logfiles (Default)[/cgeo/logfiles[PERSISTABLE_FOLDER(BASE)#1:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::/logfiles], default: (same)] (Uri: content://com.android.externalstorage.documents/tree/primary%3Acgeo/document/primary%3Acgeo%2Flogfiles, Available:true, Files: 1, subdirs:0, free space: 64,9 GB, files on device: 13278715)
- GPX: /Download (User-defined)[/Download[DOCUMENT#0:p-content://com.android.externalstorage.documents/tree/primary%3ADownload::], default: /cgeo/gpx[PERSISTABLE_FOLDER(BASE)#1:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::/gpx]] (Uri: content://com.android.externalstorage.documents/tree/primary%3ADownload/document/primary%3ADownload, Available:true, Files: 88, subdirs:10, free space: 64,9 GB, files on device: 13278715)
- BACKUP: /cgeo/backup (Default)[/cgeo/backup[PERSISTABLE_FOLDER(BASE)#1:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::/backup], default: (same)] (Uri: content://com.android.externalstorage.documents/tree/primary%3Acgeo/document/primary%3Acgeo%2Fbackup, Available:true, Files: 25, subdirs:8, free space: 64,9 GB, files on device: 13278715)
- FIELD_NOTES: /cgeo/field-notes (Default)[/cgeo/field-notes[PERSISTABLE_FOLDER(BASE)#1:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::/field-notes], default: (same)] (Uri: content://com.android.externalstorage.documents/tree/primary%3Acgeo/document/primary%3Acgeo%2Ffield-notes, Available:true, Files: 28, subdirs:0, free space: 64,9 GB, files on device: 13278715)
- SPOILER_IMAGES: /cgeo/GeocachePhotos (Default)[/cgeo/GeocachePhotos[PERSISTABLE_FOLDER(BASE)#1:p-content://com.android.externalstorage.documents/tree/primary%3Acgeo::/GeocachePhotos], default: (same)] (Uri: content://com.android.externalstorage.documents/tree/primary%3Acgeo/document/primary%3Acgeo%2FGeocachePhotos, Available:true, Files: 0, subdirs:0, free space: 64,9 GB, files on device: 13278715)
- TEST_FOLDER: [Legacy]/data/user/0/cgeo.geocaching/files/unittest (Default)[/data/user/0/cgeo.geocaching/files/unittest[FILE#1:p-file:///data/user/0/cgeo.geocaching/files::/unittest], default: (same)] (Uri: file:///data/user/0/cgeo.geocaching/files/unittest, Available:true, Files: 0, subdirs:0, free space: 64,9 GB, files on device: -1)
- Map render theme path: 
- PersistedDocumentUris: #1
- TRACK: null
- Persisted Uri Permissions: #4
- content://com.android.externalstorage.documents/tree/0123-4567%3ALocus%2FmapsVector%2F_themes (24 Feb, 16:29):RW
- content://com.android.externalstorage.documents/tree/primary%3ADownload (7 Feb, 14:47):RW
- content://com.android.externalstorage.documents/tree/primary%3Acgeo (7 Feb, 14:44):RW
- content://com.android.externalstorage.documents/tree/0123-4567%3ALocus%2FmapsVector (7 Feb, 14:46):RW
- Database: /data/user/0/cgeo.geocaching/databases/data (v94, Size:322,6 MB) on system internal storage
 -Settings: v5, Count:225
--- End of system information ---

Additional context: Tried with different themes folders (like e. g. ...\_themes, ...\_themes\Elevate and ...\_themes\Elevate\Elevate4), but to no avail.