Core/Scripts: Professor Putricide - Fixed Tear Gas spell sometimes dont casted in phase transitions (#18425)

Closes: #7972

src/server/scripts/Northrend/IcecrownCitadel/boss_professor_putricide.cpp

@@ -340,6 +340,9 @@ class boss_professor_putricide : public CreatureScript
 
             void DamageTaken(Unit* /*attacker*/, uint32& /*damage*/) override
             {
+                if (me->HasUnitState(UNIT_STATE_CASTING))
+                    return;
+
                 switch (_phase)
                 {
                     case PHASE_COMBAT_1: