Some tileset sprites have a strange transparency effect applied when city view is open

[daavko]

Describe the bug When a city view is open, some sprites (I've noticed this with units, cities, and some tile extras so far) become partially transparent.

To Reproduce Steps to reproduce the behavior:

1. Observe a unit
2. Open a city view
3. Observe the same unit, now half transparent

Expected behavior They shouldn't be half-transparent

Screenshots Regular view:

With city view open:

Platform and version (please complete the following information):

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

Additional context It seems like it applies to units regardless of where they are, but for cities and tile extras only if those are outside of the worked area of the currently opened city.