Colour picker pick colour from game window button doesn't work (on Linux)

[hhyyrylainen]

Instead I get spam like:

ERROR: Unhandled XServer error: BadMatch (invalid parameter attributes)
   Major opcode of failed request: 73
   Serial number of failed request: 0
   Current serial number in output stream: 73757
   at: default_window_error_handler (platform/linuxbsd/x11/display_server_x11.cpp:1108)

Might be Linux specific, and probably an engine issue.

• Colour picker works
• When implemented test that it works at non-default window size (to make sure this didn't get broken when switching to the Godot standard one)