Forbid empty aspects
Accidentally we revealed a bug when using an empty aspect. Weaver failed because of this empty aspect was first in the list of aspects for concatenation while it examined the last line from all aspects to append a new line symbol for files that do not end up with it. From the other side, it has no sense to provide empty aspects at all since they just occupy redundant place and do nothing useful. Some users can think that all C models should have the appropriate aspects, but this is not the case. If one does not need to weave in anything, e.g. when one provide function definitions for external undefined functions, it is enough to develop C models without aspects.