Scripts/VioletHold: Fix crash

Fix crash in Violet Hold happening when crystals were activated without killing trash mobs.
Crash added in cba6515acb5820af5df6b77855464c29062b8c44 and f4531c5a582cae24d4d136035074d8da7e5bdad7 .
Closes #14629

1 files changed, 3 insertions, 1 deletions

diff --git a/src/server/scripts/Northrend/VioletHold/instance_violet_hold.cpp b/src/server/scripts/Northrend/VioletHold/instance_violet_hold.cpp
index ea50969ecb8..ef9ad806c89 100644
--- a/src/server/scripts/Northrend/VioletHold/instance_violet_hold.cpp
+++ b/src/server/scripts/Northrend/VioletHold/instance_violet_hold.cpp
@@ -794,9 +794,11 @@ public:
             trigger->CastSpell(trigger, spellInfoLightning, true, 0, 0, trigger->GetGUID());
 
             // Kill all mobs registered with SetGuidData(ADD_TRASH_MOB)
-            for (GuidSet::const_iterator itr = trashMobs.begin(); itr != trashMobs.end(); ++itr)
+            for (GuidSet::const_iterator itr = trashMobs.begin(); itr != trashMobs.end();)
             {
                 Creature* creature = instance->GetCreature(*itr);
+                // Increment the iterator before killing the creature because the kill will remove itr from trashMobs
+                ++itr;
                 if (creature && creature->IsAlive())
                     trigger->Kill(creature);
             }