Differentiate worker location for input and working workers in productionsites

[GunChleoc]

At the moment, Building::add_worker(Worker& w) does not distinguish between workers that are occupying a working position and workers that are in an input queue. This function is called in Worker::set_location.

This code will most likely fail if a building has the same worker type as an "input" worker and as a "worker" worker. In that case, the input workers will probably be deleted as well.
Unfortunately the PlayerImmovable given as a function parameter does not offer a way to differentiate between the two kinds of workers. To fix this, one would probably create a copy of this function specifically for production sites.

[GunChleoc (gunchleoc)]

Migrated to https://github.com/widelands/widelands/issues/1084