Index guard for turn lookup to prevent error messages

[SJuliez]

This adds an index guard to Game.getTurnForPlayer() to prevent frequent log error messages. getTurnForPlayer() is called from Client.isMyTurn() when the phase is simultaneous which is the case for the PRE_* phases (activating hidden units). A similar guard is already present for Game.getTurn() which is used for non-simultaneous phases.

Removed the synchronized as MM is not multithreaded, even when simultaneous turns are used (and please let's keep it that way)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.99%. Comparing base (6a651eb) to head (d336f19).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5846   +/-   ##
=========================================
  Coverage     28.99%   28.99%           
  Complexity    13930    13930           
=========================================
  Files          2512     2512           
  Lines        267279   267278    -1     
  Branches      47833    47833           
=========================================
  Hits          77509    77509           
+ Misses       185820   185819    -1     
  Partials       3950     3950           

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