Return map & MaplePacketEncoder & Quest status patch

Fixed null pointer issue when trying to use return scroll on maps such as Mu Lung.
Fixed a critical deadlock issue with MaplePacketEncoder.
Fixed a critical DB leak regarding player's quest status.

src/server/maps/MapleMap.java

@@ -257,6 +257,7 @@ public class MapleMap {
     }
 
     public MapleMap getReturnMap() {
+        if(returnMapId == 999999999) return this;
         return Server.getInstance().getWorld(world).getChannel(channel).getMapFactory().getMap(returnMapId);
     }