Core/Entities: Make dead units not targetable for attack again (after fc5e924138).

src/server/game/Entities/Unit/Unit.cpp

@@ -12258,6 +12258,9 @@ void Unit::ClearInCombat()
 
 bool Unit::isTargetableForAttack(bool checkFakeDeath) const
 {
+    if (!isAlive())
+        return false;
+
     if (HasFlag(UNIT_FIELD_FLAGS,
         UNIT_FLAG_NON_ATTACKABLE | UNIT_FLAG_NOT_SELECTABLE | UNIT_FLAG_OOC_NOT_ATTACKABLE))
         return false;