Crash in hamster-window-server: 'NoneType' object has no attribute 'set_cursor'

Created by: matthijskooijman

I was running the latest code, and Gnome showed me a crash report. Looking inside, I found that hamster threw an exception:

org.gnome.Hamster.WindowServer[9261]: Traceback (most recent call last):
org.gnome.Hamster.WindowServer[9261]:   File "/usr/lib/python3/dist-packages/hamster/lib/graphics.py", line 2136, in __on_mouse_move
org.gnome.Hamster.WindowServer[9261]:     self.__check_mouse(event.x, event.y)
org.gnome.Hamster.WindowServer[9261]:   File "/usr/lib/python3/dist-packages/hamster/lib/graphics.py", line 2094, in __check_mouse
org.gnome.Hamster.WindowServer[9261]:     self._window.set_cursor(gdk.Cursor(cursor))
org.gnome.Hamster.WindowServer[9261]: AttributeError: 'NoneType' object has no attribute 'set_cursor'

This happened when I was editing a running activity (IIRC I changed the title). I think I just pressed "enter" to confirm the edit (after the crash, hamster-windows-service was resarted and the edit was applied).

I know this is not so much to go on, but I wanted to at least record the backtrace somewhere. Maybe this helps someone to find the problem (or maybe others seeing the same can add more info).

This happened running commit 7138d1af, so effectively 3.0.