prevent bug if subject kill by two other subject at once

sandbox/tile/config.yaml

     look_around:
         frequency: 1
     engage:
-        frequency: 2
+        frequency: 1
     move:
         walk_ref_time: 3
         run_ref_time: 1

sandbox/tile/run.py

     simulation = TileStrategySimulation(config, map_file_path=map_file_path)
     subjects = TileStrategySubjects(simulation=simulation)
 
-    for position in ((10, 2),):
+    for position in ((10, 2), (11, 3), (11, 4), (12, 5),):
         man = TileSubject(
             config=config,
             simulation=simulation,
         )
         subjects.append(man)
 
-    for position in ((30, 14),):
+    for position in ((30, 15), (31, 16), (32, 17), (33, 18),):
         man = TileSubject(
             config=config,
             simulation=simulation,

sandbox/tile/simulation/behaviour.py

         events = list()
         events.append(FireEvent(shooter_subject_id=self.subject.id, target_position=target_position))
 
-        if kill:
+        # Must be check if target is not already dead (killed same cycle)
+        if kill and COLLECTION_ALIVE in target_subject.collections:
             target_subject.collections.remove(COLLECTION_ALIVE)
             # FIXME: Must be automatic when manipulate subject collections !
             self.simulation.collections[COLLECTION_ALIVE].remove(target_subject_id)