[Bug] Error on closing module dialog with command output panel on macOS

[nilason]

Describe the bug
Starting with wxPython 4.1.0 on macOS, closing module dialog windows (also immediately after opening the dialog, with no editing) with command output panel generates an error with following traceback:

Traceback (most recent call last):
  File "/Volumes/dev/grass/dist.x86_64-apple-
darwin19.5.0/gui/wxpython/gui_core/goutput.py", line 695, in
OnDestroy

wx.TheClipboard.Flush()
wx._core
.
wxAssertionError
:
C++ assertion ""m_open"" failed at
/Users/robind/projects/bb2/dist-osx-
py37/build/ext/wxWidgets/src/osx/carbon/clipbrd.cpp(64) in
Flush(): clipboard not open
Traceback (most recent call last):
  File "/Volumes/dev/grass/dist.x86_64-apple-
darwin19.5.0/gui/wxpython/gui_core/prompt.py", line 622, in
OnDestroy

wx.TheClipboard.Flush()
wx._core
.
wxAssertionError
:
C++ assertion ""m_open"" failed at
/Users/robind/projects/bb2/dist-osx-
py37/build/ext/wxWidgets/src/osx/carbon/clipbrd.cpp(64) in
Flush(): clipboard not open

System description (please complete the following information):

• Operating System: macOS
• GRASS GIS version: 7.9.dev
• Python 3.7.3
• wxPython 4.1.0 osx-cocoa (phoenix) wxWidgets 3.1.4

Additional context
May be related to #785, but it doesn't seem to. It might also be a wxPython+mac issue.

[nilason]

Apparently, according to wxWidgets the macro causing this message:

Checks that the condition is true, returns with the given return value if not (stops execution in debug mode).
This check is done even in release mode.
This macro may be only used in non-void functions, see also wxCHECK_RET().
This macro should be used to catch (both in debug and release builds) logical errors done by the programmer.

It is thrown here.

Either the clipboard should be opened and the fix would be to correct that, alternatively the wx.TheClipboard.Flush() could be put in a if-clause if wx.TheClipboard.IsOpened():. I'm not sure what the expected behaviour should be.