Rush buying a unit shows complete in 2 turns

[jwrober]

Describe the bug
Not always, there is some condition that occurs that when you rush buy a unit the client will show 2 turns to finish and zero gold. The unit is finished at turn change as expected, but the city dialog shows an incorrect value.

To Reproduce
Steps to reproduce the behavior:

1. Open a game
2. Open a city building a unit such as a Caravan
3. Rush buy the unit
4. See error -- note that it does not happen at all times

Expected behavior
The city dialog shows correct values

Screenshots

Platform and version (please complete the following information):

• OS: Linux
• Freeciv21 version: 3.1-dev, and in 3.0-rc.2
• Ruleset/Longturn game (if applicable): Discovered in LTX LT76Teams, so don't know if its a rules thing or a client thing for sure.

Additional context
Add any other context about the problem here.

[lmoureaux]

To be more specific, it shows the number of turns to completion before buying, as if the client was unaware of the gold it spent.