Unit/PlayerAI: Yeah, we allow charmer to be null now, should probably check for that.

Fixes and closes #16728.

(cherry picked from commit 49de12b1cf)

src/server/game/AI/PlayerAI/PlayerAI.cpp

@@ -147,6 +147,8 @@ Unit* SimpleCharmedPlayerAI::SelectAttackTarget() const
 void SimpleCharmedPlayerAI::UpdateAI(const uint32 /*diff*/)
 {
     Creature* charmer = me->GetCharmer() ? me->GetCharmer()->ToCreature() : nullptr;
+    if (!charmer)
+        return;
 
     //kill self if charm aura has infinite duration
     if (charmer->IsInEvadeMode())