[#3250|Console] Fix errors dispaying magnets with no files

Trying to display the files for magnet that has no metadata and thus no
files resulted in `'NoneType' object is not iterable` errors.

Only call file prio update method if we have a list of files.

deluge/ui/console/modes/torrentdetail.py

@@ -212,7 +212,7 @@ class TorrentDetail(BaseMode, PopupsHandler):
             if self.file_dict[i][6] != prio:
                 need_prio_update = True
                 self.file_dict[i][6] = prio
-        if need_prio_update:
+        if need_prio_update and self.file_list:
             self.__fill_prio(self.file_list)
         del state['file_progress']
         del state['file_priorities']