gitea: Regression: login via LDAP not possible: '(LDAP Result Code 2 "Protocol Error": )'

• Gitea version (or commit ref): dfad569 built with go1.11.5 : bindata, sqlite, sqlite_unlock_notify
• Git version: 2.18.1
• Operating system: offical docker image, docker.io/gitea/gitea, tag 1.7, image ID 044ab4ac3753
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist:

Description

I am not able to log in via LDAP anymore:

[...gitea/models/user.go:1544 SyncExternalUsers()] [E] LDAP Search failed unexpectedly! (LDAP Result Code 2 "Protocol Error": )

The LDAP problems came as a regression when I updated to 1.6. I thought that the backport of #5816 to 1.7.1 would solve my problems. But unfortunately this is not the case, an update of my container image to the latest 1.7 tag has the above mentioned log.