Core/Group: Fix memory leak

Fix memory leak happening when disbanding a group with an ongoing roll.
Please note this is not blizz-like but at least we don't leak memory anymore.

src/server/game/Groups/Group.cpp

@@ -794,7 +794,7 @@ void Group::Disband(bool hideDestroy /* = false */)
 
         _homebindIfInstance(player);
     }
-    RollId.clear();
+
     m_memberSlots.clear();
 
     RemoveAllInvites();