wxGUI: fix setting of user defined window position and size for single window mode

[tmszi]

Fixes #2600.

How to test this PR:

1. Launch wxGUI with single window mode
2. Change and remember visually wxGUI window size and position
3. Open wxGUI settings via menu Settings -> Preferences
4. On the General page (tab) from the Workspace setting check Save current windows layout as default
5. Hit Preferences dialog Save button
6. Close wxGUI
7. Launch wxGUI and check window position and size

If you want to change the wxGUI position and size again, you need to open the wxGUI preferences dialog again and press the Save button again.

[petrasovaa]

Works fine, thank you! I don't think the tuple comparison works well here, it's not the same thing as if w <= GM_WINDOW_SIZE[0] or h <= GM_WINDOW_SIZE[1] if that's what you meant.

[tmszi]

I don't think the tuple comparison works well here, it's not the same thing as if w <= GM_WINDOW_SIZE[0] or h <= GM_WINDOW_SIZE[1] if that's what you meant.

Yes you are right. Thank you.