Stuck in a door in dungeon 9

[christopho]

Bug report from nimaje:

Hi all,

on FreeBSD with solarus 1.5.0 (from ports) and ZSDX 1.11.0 (from git) it is posible to get locked in Dungeon 9.
You will be on the same place as a closed door.

Reproduce:
Start in dungeon 9 2F room with invisible tiles.
Fall down you should be in the north door.
Leave north
Do something that the door closes, e.g. go directly left
Go back till a room with spikes
use the feather to jump into the spikes
Now you should be in the closed door of the room with invisible tiles.