Changing the zoom level while in a city dialog causes the dialog to close

[jwrober]

Describe the bug
Changing the zoom level while in a city dialog causes the dialog to close

To Reproduce
Steps to reproduce the behavior:

1. Go to default zoom (ctrl-backspace) -- or use the view menu
2. Open a city dialog box
3. Zoom in one level (shift-+) -- or use the view menu
4. Notice the dialog closes and then the map zooms in one level

Expected behavior
The map zooms in one level and so does the city center and the city dialog's size shifts to match the new dimensions.

Screenshots
N/A

Platform and version (please complete the following information):

• OS: All
• Freeciv21 version: 3.0-Alpha9
• Ruleset/Longturn game (if applicable): N/A

Additional context
None

[lmoureaux]

This is because changing the zoom level reloads the tileset, and reloading the tileset closes the city dialog.