fix bashable furnitures not bashable by monsters

[leoCottret]

Summary

Purpose of change

Fix #1691
When a monster tries to reach the player, but has a bashable furniture that he can bash on his path, he'll try to bash it endlessly.
But the function used to bash the terrain/furniture has some bug that don't allow the monster to bash it.

More precisely, the function checks if the terrain is flat/is a road, then if it's bashable, and will stop the bashing attempt if it isn't. But it doesn't check if there is a bashable furniture on it.

This can be observed with a zombie soldier/zombie hulk and a large canvas door/animal skin wall/cardboard wall on a flat terrain

Describe the solution

Fix the function so it checks if there's is a bashable furniture on the terrain before stoping the bashing attempt.

Testing

In the same situation as the bug report, fixing the function made the zombie bash the wall at will