Add missing break in ApplyInstanceStrategies (mod-playerbots#1887)

Well, I hope nobody has tried Magtheridon lately. It looks like this got
inadvertently deleted during the merge.

Author: brighton-chi

src/PlayerbotAI.cpp

@@ -1477,6 +1477,7 @@ void PlayerbotAI::ApplyInstanceStrategies(uint32 mapId, bool tellMaster)
             break;
         case 544:
             strategyName = "magtheridon";  // Magtheridon's Lair
+            break;
         case 565:
             strategyName = "gruulslair";  // Gruul's Lair
             break;