also try to get file info from part file
don't scan part files
only set the values we need and make sure that we write the file info for both
the real file and the part file, because some information from the part file
might be needed later
Merge pull request #11736 from owncloud/enc_get_fileinfo_from_real_file

if we read a .part file we try to get the file info from the real file