Don't generate pet number twice on tame.

It's already generated and set as the entry of the ObjectGuid in CreateBaseAtCreature. Thanks to celguar for noticing this.

src/game/Spells/SpellEffects.cpp

@@ -3949,7 +3949,7 @@ void Spell::EffectTameCreature(SpellEffectIndex /*effIdx*/)
         return;
     }
 
-    pet->GetCharmInfo()->SetPetNumber(sObjectMgr.GeneratePetNumber(), true);
+    pet->GetCharmInfo()->SetPetNumber(pet->GetObjectGuid().GetEntry(), true);
     pet->GetCharmInfo()->SetReactState(REACT_DEFENSIVE);
     pet->InitializeDefaultName();
     pet->AIM_Initialize();