Core: Remove "enumeration value 'xxx' not handled in switch" warnings

--HG--
branch : trunk

src/server/game/Instances/InstanceScript.cpp

@@ -95,6 +95,8 @@ void InstanceScript::UpdateMinionState(Creature *minion, EncounterState state)
             else if (!minion->getVictim())
                 minion->AI()->DoZoneInCombat();
             break;
+        default:
+            break;
     }
 }