[Bug] g.gui.gcp: crash when closing (wx._core.wxAssertionError: C++ assertion "GetEventHandler())

[neteler]

Describe the bug

g.gui.gcp crashes with this error when closing:

...
(g.gui.gcp:551149): Gtk-WARNING **: 22:34:48.159: for_size smaller than min-size (18 < 32) while measuring gadget (node entry, owner GtkSpinButton)

(g.gui.gcp:551149): Gtk-WARNING **: 22:34:48.235: for_size smaller than min-size (18 < 32) while measuring gadget (node entry, owner GtkSpinButton)

(g.gui.gcp:551149): Gtk-WARNING **: 22:34:48.300: for_size smaller than min-size (18 < 32) while measuring gadget (node entry, owner GtkSpinButton)

(g.gui.gcp:551149): Gtk-WARNING **: 22:34:48.351: for_size smaller than min-size (18 < 32) while measuring gadget (node entry, owner GtkSpinButton)

(g.gui.gcp:551149): Gtk-WARNING **: 22:34:48.404: for_size smaller than min-size (18 < 32) while measuring gadget (node entry, owner GtkSpinButton)
Traceback (most recent call last):
  File "/home/mneteler/software/grass78_git/dist.x86_64-pc-linux-gnu/scripts/g.gui.gcp", line 71, in <module>
    main()
  File "/home/mneteler/software/grass78_git/dist.x86_64-pc-linux-gnu/scripts/g.gui.gcp", line 68, in main
    app.MainLoop()
  File "/usr/lib64/python3.7/site-packages/wx/core.py", line 2166, in MainLoop
    rv = wx.PyApp.MainLoop(self)
wx._core.wxAssertionError: C++ assertion "GetEventHandler() == this" failed at ../src/common/wincmn.cpp(477) in ~wxWindowBase(): any pushed event handlers must have been removed

System description (please complete the following information):

• Operating System: Fedora 31
• GRASS GIS version:

g.version -rge
version=7.8.3dev
date=2020
revision=42388e55e
build_date=2020-03-15
build_platform=x86_64-pc-linux-gnu
build_off_t_size=8
libgis_revision=
libgis_date=
WARNING: GRASS GIS libgis version and date number not available
proj=5.2.0
gdal=2.3.2
geos=3.7.1
sqlite=3.30.0