Fullscreen view doesn't remember previous maximization state

[daavko]

Describe the bug
After entering fullscreen while the window is maximized and exiting fullscreen, the window is not maximized anymore.

To Reproduce
Steps to reproduce the behavior:

1. Maximize the game window
2. Enter fullscreen
3. Exit fullscreen

Expected behavior
The window should remember whether it was maximized or not when leaving fullscreen and enter that state.

Platform and version (please complete the following information):

• OS: Windows 10
• Freeciv21 version: beta 2
• Ruleset/Longturn game (if applicable): not applicable

Additional context
No additional context