wxGUI/dbmgr: do not modify layer settings if settings have not changed

[tmszi]

Describe the bug
The wxGUI Attribute Table Manager adjusts the layer settings even if the settings have not changed while pressing the Modify layer button.

To Reproduce
Steps to reproduce the behavior:

1. Launch Attribute Table Manager e.g. g.gui.dbmgr geology
2. On the Attribute Table Manager window switch to the Manage Layers page (tab)
3. On the Manage Layers page (tab) switch to the Modify layer page (tab)
4. Do not change layer settings
5. Hit Modify layer button
6. See error

Traceback (most recent call last):
  File "/usr/lib64/grass84/gui/wxpython/dbmgr/base.py", line 3896, in OnModifyLayer
    self.parentDialog.parentDbMgrBase.UpdateDialog(layer=layer)
  File "/usr/lib64/grass84/gui/wxpython/dbmgr/manager.py", line 253, in UpdateDialog
    DbMgrBase.UpdateDialog(self, layer=layer)
  File "/usr/lib64/grass84/gui/wxpython/dbmgr/base.py", line 854, in UpdateDialog
    self.pages["browse"].DeletePage(layer)
  File "/usr/lib64/grass84/gui/wxpython/dbmgr/base.py", line 1023, in DeletePage
    self.selLayer = self.layers[self.GetSelection()]
IndexError: list index out of range

Expected behavior
The wxGUI Attribute Table Manager don't adjusts the layer settings if the settings have not changed while pressing the Modify layer button.

System description (please complete the following information):

• Operating System: all
• GRASS GIS version: all

GRASS nc_basic_spm_grass7/PERMANENT:~ > python3 -c "import sys, wx; print(sys.version); print(wx.version())"
3.10.13 (main, Aug 25 2023, 20:13:27) [GCC 12.3.1 20230526]
4.2.0 gtk3 (phoenix) wxWidgets 3.2.2.1

Additional context
Issue related to incorrectly evaluated if condition (layer settings changed), especially line 3863 self.modifyLayerWidgets["database"][1].GetStringSelection().

Layer Database setting is TextCtrl widget and self.modifyLayerWidgets["database"][1].GetStringSelection() code especially GetStringSelection() method return empty string. Correct method for return control value should be GetValue().

grass/gui/wxpython/dbmgr/base.py

Lines 3860 to 3870 in db8c58f

	if (
	self.modifyLayerWidgets["driver"][1].GetStringSelection()
	!= self.mapDBInfo.layers[layer]["driver"]
	or self.modifyLayerWidgets["database"][1].GetStringSelection()
	!= self.mapDBInfo.layers[layer]["database"]
	or self.modifyLayerWidgets["table"][1].GetStringSelection()
	!= self.mapDBInfo.layers[layer]["table"]
	or self.modifyLayerWidgets["key"][1].GetStringSelection()
	!= self.mapDBInfo.layers[layer]["key"]
	):
	modify = True