fix(Scripts/UBRS): fix crash with Solakar minions (#10638)

src/server/scripts/EasternKingdoms/BlackrockMountain/BlackrockSpire/instance_blackrock_spire.cpp

@@ -362,7 +362,10 @@ public:
                         case FAIL:
                             for (const auto& creature : SolakarSummons)
                             {
-                                creature->RemoveFromWorld();
+                                if (creature)
+                                {
+                                    creature->RemoveFromWorld();
+                                }
                             }
                             SolakarSummons.clear();
                             CurrentSolakarWave = 0;