added null check for lastUnitMember

[DM0000]

closes #6211.

Check to see if lastUnit.next() is null before trying to setUnitNumber doing entityUpdate.
Fixed crash when removing protos in provided mul and was able to deploy force

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.18%. Comparing base (a28fd13) to head (204c1f5).
Report is 49 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6212      +/-   ##
============================================
+ Coverage     29.09%   29.18%   +0.08%     
+ Complexity    13981    13980       -1     
============================================
  Files          2647     2628      -19     
  Lines        267373   266566     -807     
  Branches      47650    47577      -73     
============================================
- Hits          77793    77789       -4     
+ Misses       185696   184896     -800     
+ Partials       3884     3881       -3     

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