libtracker-miner: Ensure TrackerFileSystem has a meaningful file type
libtracker-miner: Ensure TrackerFileSystem has a meaningful file type

tracker_file_system_get_file() will be called several times on the
same file, so store the first meaningful GFileType gotten through
that call.

outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker