PICARD-1914: When file gets unlinked from track update metadata box

Prevents editing the metadata for the track still alters the file.

picard/track.py

@@ -186,6 +186,9 @@ class Track(DataObject, Item):
         remove_metadata_images(self, [file])
         run_file_post_removal_from_track_processors(self, file)
         self.update()
+        if self.item.isSelected():
+            self.tagger.window.metadata_box.selection_dirty = True
+            self.tagger.window.metadata_box.update()
 
     def update(self):
         if self.item: