Core/Misc: Fix some static analysis issues

Fix some static analysis issues about missing NULL checks.
Pass safe Creature pointer instead of summoning a Creature, passing the GUID and retrieve the same Creature from GUID.

src/server/game/Handlers/PetHandler.cpp

@@ -718,6 +718,12 @@ void WorldSession::HandlePetSpellAutocastOpcode(WorldPacket& recvPacket)
     }
 
     SpellInfo const* spellInfo = sSpellMgr->GetSpellInfo(spellid);
+    if (!spellInfo)
+    {
+        TC_LOG_ERROR("network", "WORLD: unknown PET spell id %u", spellid);
+        return;
+    }
+
     // do not add not learned spells/ passive spells
     if (!pet->HasSpell(spellid) || !spellInfo->IsAutocastable())
         return;

src/server/scripts/EasternKingdoms/Karazhan/karazhan.cpp

@@ -614,7 +614,8 @@ public:
                 }
                 return 50000;
             case 15:
-                arca->DealDamage(arca, arca->GetHealth(), NULL, DIRECT_DAMAGE, SPELL_SCHOOL_MASK_NORMAL, NULL, false);
+                if (arca)
+                    arca->DealDamage(arca, arca->GetHealth(), NULL, DIRECT_DAMAGE, SPELL_SCHOOL_MASK_NORMAL, NULL, false);
                 return 5000;
             default : return 9999999;
             }

src/server/scripts/Northrend/zone_zuldrak.cpp

@@ -57,16 +57,15 @@ public:
             float x, y, z;
             me->GetClosePoint(x, y, z, me->GetObjectSize() / 3, 0.1f);
 
-            if (Unit* summon = me->SummonCreature(NPC_RAGECLAW, x, y, z, 0, TEMPSUMMON_DEAD_DESPAWN, 1000))
+            if (Creature* summon = me->SummonCreature(NPC_RAGECLAW, x, y, z, 0, TEMPSUMMON_DEAD_DESPAWN, 1000))
             {
                 _rageclawGUID = summon->GetGUID();
-                LockRageclaw();
+                LockRageclaw(summon);
             }
         }
 
-        void LockRageclaw()
+        void LockRageclaw(Creature* rageclaw)
         {
-            Unit* rageclaw = Unit::GetCreature(*me, _rageclawGUID);
             // pointer check not needed
             me->SetInFront(rageclaw);
             rageclaw->SetInFront(me);
@@ -75,12 +74,11 @@ public:
             DoCast(rageclaw, SPELL_RIGHT_CHAIN, true);
         }
 
-        void UnlockRageclaw(Unit* who)
+        void UnlockRageclaw(Unit* who, Creature* rageclaw)
         {
             if (!who)
                 return;
 
-            Creature* rageclaw = Unit::GetCreature(*me, _rageclawGUID);
             // pointer check not needed
             DoCast(rageclaw, SPELL_FREE_RAGECLAW, true);
 
@@ -95,7 +93,7 @@ public:
                 {
                     if (Creature* rageclaw = Unit::GetCreature(*me, _rageclawGUID))
                     {
-                        UnlockRageclaw(caster);
+                        UnlockRageclaw(caster, rageclaw);
                         caster->ToPlayer()->KilledMonster(rageclaw->GetCreatureTemplate(), _rageclawGUID);
                         me->DespawnOrUnsummon();
                     }