Core/Dungeon Finder: Return a copy of cached dungeons set (to avoid being cleared later in code)

--HG--
branch : trunk

src/server/game/DungeonFinding/LFGMgr.h

@@ -313,7 +313,7 @@ class LFGMgr
         LfgLockStatusSet* GetPlayerLockStatusDungeons(Player* plr, LfgDungeonSet& dungeons, bool useEntry);
 
         // Generic
-        void GetDungeonsByRandom(uint32 randomdungeon, LfgDungeonSet& dungeons);
+        LfgDungeonSet GetDungeonsByRandom(uint32 randomdungeon);
         LfgType GetDungeonType(uint32 dungeon);
         std::string ConcatenateGuids(LfgGuidList check);