Fix MHQ #4002: prevent infinite loop while assigning SPAs by removing unusable entries

[Sleet01]

Note: this may fix #4002, or may only fix something that may be contributing to it.

Prevent infinite loop by reducing choices each time we continue the while loop.
Also remove a check for more elements in some SPAs that, honestly, I don't remember writing - it actively prevents some SPAs from being applied even if they are valid.

Testing:

• Tested with failing save from 49.19 Nightly - Soft Freeze upon advancing day. #4002;
• Add unit tests for large number of consecutive calls to the previously-failing function;
• Ran all 3 projects' unit tests as well.

[kuronekochomusuke]

this fixed the freeze I was getting following IllianiCBT's steps to reproduce the issue