Fix import for existing parent listings.

librestash/lib/adaptors/gpx.py

@@ -124,6 +124,8 @@ class GpxImporter(object):
                     logger.info('Creating new master waypoint and listing for %s' % parent_code)
                     parent_waypoint = Waypoint(code=parent_code)
                     parent_listing = Listing(master_waypoint=parent_waypoint, waypoints=[parent_waypoint])
+                else:
+                    parent_listing = parent_waypoint.listing
 
                 # Add waypoint
                 logger.info('Linking %s to %s' % (waypoint.code, parent_code))