Stop generated monsters stacking.

A check for $ row/col of the monster requesting the move was allowing
generated monsters (which don't have row/col defined) to be placed on
top of existing monsters. The values are only required to determine if
the monster is moving towards or away from the monster being asked if
the move is ok, and are not needed for generated mobs. ReqSomethingMoved
will now return FALSE if the requesting monster tries to land on top of
the requested one.