Error when subject is missing surface map or map is incomplete

[slamballais]

QDECR checks whether subject directories exist, but doesn't separately check whether the surface files exist. Furthermore, it doesn't check whether the file has an appropriate number of vertices. Two extra checks need to be added.

[slamballais]

I implemented a check on whether files exist in 306826c

I decided not to implement a check for the number of vertices. This would require the creation and deletion of an intermediate object in memory for every person that is loaded in, which is a very high burden for a rare occurrence.