wxGUI/psmap: don't set StatusBar widget text when frame is closed

[tmszi]

Describe the bug
When map preview is rendered and Cartographic Composer frame is closed, error message is printed.

To Reproduce
Steps to reproduce the behavior:

1. Launch wxGUI Cartographic Composer g.gui.psmap
2. From the toolbar activate Map frame tool and add raster map e.g. elevation
3. From the toolbar hit Show preview tool
4. From the toolbar hit Show preview tool again
5. Close the Cartographic Composer window
6. See error

Traceback (most recent call last):
  File "/home/tomas/.local/lib/python3.9/site-
packages/wx/core.py", line 2254, in Notify

self.notify()
  File "/home/tomas/.local/lib/python3.9/site-
packages/wx/core.py", line 3410, in Notify

self.result = self.callable(*self.args, **self.kwargs)
  File "/usr/lib64/grass83/gui/wxpython/psmap/frame.py",
line 517, in <lambda>

self.delayedCall = wx.CallLater(4000, lambda:
self.SetStatusText("", 0))
RuntimeError
:
wrapped C/C++ object of type PsMapFrame has been deleted

Expected behavior
When map preview is rendered and Cartographic Composer frame is closed, error message should not be printed.

System description (please complete the following information):

• Operating System: all
• GRASS GIS version: all