wxGUI: fix show MASK statusbar button widget if mask is created

[tmszi]

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Describe the bug The main wxGUI statusbar MASK button widget is not showed when new MASK map is created.

To Reproduce Steps to reproduce the behavior:

1. Install Python watchdog library via your distribution package manager or via pip install watchdog
2. Remove MASK if exists r.mask -r
3. Launch wxGUI
4. Create some MASK e.g. r.mask elevation
5. Main wxGUI statusbar MASK button widget is not showed

Expected behavior If new MASK map is created, main wxGUI statusbar MASK button widget should be showed.

System description:

• Operating System: all
• GRASS GIS version: 8.3.dev, 8.2