Fix #6259 error spam and deployment hang with combined arms forces

[Sleet01]

This clears up some error spam and Exceptions reported in #6259. Also fixed a log line that was not getting formatted correctly.

Hopefully also prevents hung games on rare occasions where the deployment hex scoring process and/or path-generating process could result in a null return value, possibly hanging the game (I was not able to reproduce this error after making these changes).

Of note, changes previously made to prevent ConcurrentModificationException errors had to be reinforced with explicit synchronized(modes) blocks, possibly due to more checks introduced via the Pulse Module updates. Keep this approach in mind for similar issues seen due to iterator usage causing fail-fast errors.

Testing:

1. ran mission from issue dozens of times.
2. ran all projects' unit tests.

Close #6259

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.95%. Comparing base (ba6cfe2) to head (5bcc422).
Report is 8 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6292      +/-   ##
============================================
- Coverage     28.95%   28.95%   -0.01%     
+ Complexity    14018    14016       -2     
============================================
  Files          2672     2672              
  Lines        269229   269237       +8     
  Branches      47911    47913       +2     
============================================
- Hits          77953    77950       -3     
- Misses       187376   187387      +11     
  Partials       3900     3900              

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