Crash if Preferences window is closed by Close button

[slsimic]

System Details:

• Operating System: LINUX

• Distro(For GNU/Linux and BSD users): SolydK 10 (Debian Buster based)

• Desktop Environment(For GNU/Linux and BSD users): KDE Plasma

• Persepolis Version: 3.0.1

• How do you install Persepolis? Debian Buster repository

• Please attach log files if crash or paste error message Output from console>

  
  slobodan@solydk:~$ persepolis 
  qt5ct: using qt5ct plugin
  qt5ct: D-Bus global menu: no
  qt5ct: D-Bus system tray: yes
  qt.qpa.xcb: QXcbConnection: XCB error: 5 (BadAtom), sequence: 709, resource id: 0, major code: 19 (DeleteProperty), minor code: 0
  KCrash: crashing... crashRecursionCounter = 2
  KCrash: Application Name = python3.7 path = /usr/bin pid = 15438
  KCrash: Arguments: /usr/bin/python3.7 
  KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi from kdeinit
  sock_file=/run/user/1000/kdeinit5__0

[1]+ Заустављен persepolis slobodan@solydk:~$ QSocketNotifier: Invalid socket 10 and type 'Read', disabling... QSocketNotifier: Invalid socket 14 and type 'Read', disabling... QSocketNotifier: Invalid socket 11 and type 'Read', disabling...

[1]+ Изађи из „253“ persepolis

**Issue Description and steps to reproduce:**

Persepolis (or more accurate, python 3.7) crashes every time Preferences window is closed by clicking on window Close button, no matter if there is a changes made or not. When the Preferences window is closed by Cancel or OK button, everything is fine