Bug and fix - crashes when deleting signs using the way removal tool

[jamespetts]

This issue has been reported, and now fixed, in Experimental, but my inspection of the Standard code shows that the problem may well be present there, too, although I have not had time to test it.

The problem occurred when a sign or signal was present on a way tile which was also a junction, and the way removal tool was used to remove the way going in one direction from that tile but not the way going in the other direction. When a sign or signal appeared on that tile, that sign or signal would be removed, too, but the count_signs() method would not be called on the remaining tile with the result that the has_sign() method would return true even though there is no sign on the tile, resulting in access violations/segmentation faults when a vehicle calculated its route and tried to check what sort of sign was present.

this fix should do it, by calling count_signs() on any way tiles left after deletion. My tests show that this prevents the crash in Experimental. Another option would be not to remove the sign in this case: consideration will have to be given as to whether this is the better behaviour.

[prissi]

Considering that signs or signals are not allowed on crossings (at least directional one will neither display nor work correct), full removal make sense for me.