Unnecessary checkout for getting file size, Fixes: #2303

Changes the unnecessary checkout for get the file size from joural.
This search in self._metadata the filesize file if this is in self._metadata this send a file(filesize) with self._metadata.get('filesize') and if filesize is not in self._metadata(else) this send a file(filesize) with model.get_file_size(self._metadata['uid']) and print in lines _('Size: %s') % (format_size(int(filesize)))