Very slow when quitting gedit with restore between sessions enabled

[jefferyto]

If "Restore windows between sessions" is enabled, there is a noticeable delay from when quit is activated to when the application has finally exited. gedit is not responsive during this time.

This behaviour exists in gedit 3.30.2 and older (down to 3.12), and the problem seems more pronounced when multiple documents and/or windows are open (at the time of quitting).

The issue is so large that sometimes window managers / desktop environments (e.g. GNOME) may even consider gedit to have stopped responding and prompt the user to force-quit the application.

I don't have enough time right now to fully investigate this (indeed I'm not even entirely sure how to do this investigation), but this is something that needs to be fixed.