godot: X11: Cursor in captured mode is broken for devices working in absolute mode

Godot version:

f50dd682f6a0f9506daaf16fed06f4bc9efa6599

OS/device including version:

Linux / Ubuntu 18.04.1 LTS

Issue description: Steps to reproduce:

Set e.g. Wacom pen in absolute mode with the Gnome settings-panel or:

xsetwacom --set Wacom Intuos4 4x6 Pen stylus Mode Absolute
xsetwacom --set Wacom Intuos4 4x6 Pen stylus Area 0 0 31496 9842
xsetwacom --set Wacom Intuos4 4x6 Pen stylus MapToOutput desktop

The cursor leaves our planet:

Minimal reproduction project:

Modified example from https://github.com/godotengine/godot/issues/21744 (thanks!): i21744-Constrained-Cursor.zip