fix cuts for multipart videos

pandora/item/timelines.py

@@ -117,7 +117,9 @@ def join_tiles(source_paths, target_path):
             mode = info['mode']
             source_files[mode].append(path + info['file'])
     modes = [m for m in modes if source_files[m]]
+    for i, path in enumerate(source_paths):
         for f in source_files[modes[0]]:
+            if f.startswith(path):
                 width = Image.open(f).size[0]
                 durations[i] += width / fps
                 frame_n += width