Core/AI: Fix creatures not updating their target properly once engaged

Closes  #21562

(cherry picked from commit 7fb74326205acbc5c0fa6b2aa9731d891e788d64)

src/server/game/AI/SmartScripts/SmartAI.cpp

@@ -285,6 +285,8 @@ void SmartAI::UpdateAI(uint32 diff)
 
     CheckConditions(diff);
 
+    bool hasVictim = UpdateVictim();
+
     GetScript()->OnUpdate(diff);
 
     UpdatePath(diff);
@@ -294,7 +296,7 @@ void SmartAI::UpdateAI(uint32 diff)
     if (!IsAIControlled())
         return;
 
-    if (!UpdateVictim())
+    if (!hasVictim)
         return;
 
     if (_canAutoAttack)