[BUG] horses can get stuck at the beginning of stairs

[Juknum]

When a player doesn't have eaten anybody, the horse continues its course along its path, but after 2 or more lap, the horse gets stuck at the beginning of its stairs.

How to reproduce
For an easier way to reproduce this, follow those steps:

1. set DEBUG to true in Constants.java
2. set NB_HORSE at 1 in Constants.java
3. deactivate the eating process (set in to false)
4. see horses walking forever, until being stuck

Expected behaviour
Horses should walk forever without getting stuck.