Information widgets open multiple times

[daavko]

Describe the bug Every time a player either clicks the menu item or uses a keyboard shortcut to open "Wonders of the world", "Top 5 cities", or "Demographics", a new widget is opened each time, even if there is one already open.

To Reproduce Steps to reproduce the behavior:

1. Click on, for example, "Demographics" in the menu or use a keyboard shortcut to open it
2. Do step 1 again
3. Do step 1 again
4. Observe 3 identical widgets of demographics

Expected behavior It should either only ever open one widget, or close the opened widget like the Units widget does.

Screenshots

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