It wasn't fine to call core.open_doc without filename argument
and later call Doc:save without providing both the filename and
the absolute filename. It was giving a Doc in an inconsistent
status where self.filename was set but not self.abs_filename.
Added an asset to detect early the problem if ever happens again.
In turn the problem prevented the project's module hook to work if the
file was newly created.
Francesco Abbate
fd074ff39a