Core/Spells: Fix a small proc-issue with hunter T10 set bonuses (Exploit Weakness)

(original fix by Dr.Tenma)
Comment issue #4362
From DBCs TargetA[0] is already set as TARGET_UNIT_PARTY_CASTER, which maps to TARGET_UNIT_CASTER,
so it should be enough to explicitly target the casters pet in this case, ie. just doing
spellInfo->EffectImplicitTargetB[0] = TARGET_UNIT_PET; - feedback on this required.

--HG--
branch : trunk

src/server/game/Spells/SpellMgr.cpp

@@ -3889,6 +3889,10 @@ void SpellMgr::LoadSpellCustomAttr()
             spellInfo->targetAuraSpell = 0;
             count++;
             break;
+        case 70728: // Exploit Weakness
+            spellInfo->EffectImplicitTargetB[0] = TARGET_UNIT_PET;
+            count++;
+            break;
         case 71413: // Green Ooze Summon
         case 71414: // Orange Ooze Summon
             spellInfo->EffectImplicitTargetA[0] = TARGET_DEST_DEST;