Core/PetAI: Fix memory leak

Fix memory leak added in e7f0808d46

Valgrind log:
395,712 (390,216 direct, 5,496 indirect) bytes in 229 blocks are definitely lost in loss record 65 of 67
 at operator new(unsigned long) (vg_replace_malloc.c:320)
 by PetAI::UpdateAI(unsigned int) (PetAI.cpp:167)
 by Creature::Update(unsigned int) (Creature.cpp:541)
 by TempSummon::Update(unsigned int) (TemporarySummon.cpp:47)

src/server/game/AI/CoreAI/PetAI.cpp

@@ -183,7 +183,11 @@ void PetAI::UpdateAI(uint32 diff)
                 }
 
                 if (spellInfo->HasEffect(SPELL_EFFECT_JUMP_DEST))
+                {
+                    if (!spellUsed)
+                        delete spell;
                     continue; // Pets must only jump to target
+                }
 
                 // No enemy, check friendly
                 if (!spellUsed)