Picking a ruleset can override the number of players

[jwrober]

Describe the bug While setting up a new game, a user can set the number of players they want to play with and then pick a ruleset to play. If the ruleset sets the number of players, it will override what a user has picked already.

To Reproduce Steps to reproduce the behavior:

1. Start the client
2. Click on start a new game
3. Use the number of players spinner to make the total number of players greater than 5 ( I used 10)
4. Pick Civ1 from the rules drop down box
5. Notice number of players is now set to 5.

Expected behavior Don't override what the user has done, or at least ask before changing the setting

Screenshots N/A

Platform and version (please complete the following information):

• OS: Linux
• Freeciv21 version: 3.0-beta3
• Ruleset/Longturn game (if applicable): N/A

Additional context None

[lmoureaux]

Closely related to #1625.