[Hamlet] Pig thief's map is useless when read indoors.

I once read a pig thief's map when I was in a house (the bank). Then the map "revealed“at a nowhere. No secret camp revealed and the map focused at a place which far away from any islands. 

I know that enter a room is just teleport the player to somewhere away from the main map. So maybe we can just stop players read the map when indoor?