wxGUI/gmodeler: fix storing current model settings to model file

[tmszi]

Describe the bug
Saving the Graphical Modeler current model settings to model file fails and prints an error message if Graphical Modeler window is closed.

To Reproduce
Steps to reproduce the behavior:

1. Launch Graphical Modeler g.gui.gmodeler
2. Add GRASS tool (module) to model e.g. simple module command db.test test1
3. Validate model
4. Run model
5. Close Graphical Modeler window by keyboard shortcut Alt + F4 or via toolbar Quit tool
6. On the confirm save current model settings to model file dialog hit Yes button
7. See error

Traceback (most recent call last):
  File "/usr/lib64/grass84/gui/wxpython/gmodeler/frame.py", line 373, in OnCloseWindow
    self.OnWorkspaceSaveAs()
AttributeError: 'ModelFrame' object has no attribute 'OnWorkspaceSaveAs'

Expected behavior
Saving Graphical Modeler current model settings to model file should work and not printing an error message if Graphical Modeler window is closed.

System description:

• Operating System: all
• GRASS GIS version: all

GRASS nc_spm_08_grass7/PERMANENT:~ > python3 -c "import sys, wx; print(sys.version); print(wx.version())"
3.10.13 (main, Sep 16 2023, 22:24:59) [GCC 12.3.1 20230526]
4.2.0 gtk3 (phoenix) wxWidgets 3.2.2.1