Update album images when an album is to be shown

When a user drops different images to be used as covers of
different tracks of the same album, the album's metadata.images list
didn't reflect these changes. This commit updates the list of images
so CoverArtBox always shows the correct values

picard/album.py

@@ -557,6 +557,19 @@ class Album(DataObject, Item):
             self.tagger.albums[mbid] = self
             self.load(priority=True, refresh=True)
 
+    def update_metadata_images(self):
+        new_images = []
+        for track in self.tracks:
+            for file in list(track.linked_files):
+                for image in file.metadata.images:
+                    if image not in new_images:
+                        new_images.append(image)
+        for file in list(self.unmatched_files.files):
+            for image in file.metadata.images:
+                if image not in new_images:
+                    new_images.append(image)
+        self.metadata.images = new_images
+
 
 class NatAlbum(Album):
 

picard/ui/mainwindow.py

@@ -952,6 +952,10 @@ class MainWindow(QtGui.QMainWindow):
                         }
                     self.set_statusbar_message(msg, mparms, echo=None,
                                                history=None)
+            elif isinstance(obj, Album):
+                obj.update_metadata_images()
+                metadata = obj.metadata
+                orig_metadata = obj.orig_metadata
             elif obj.can_edit_tags():
                 metadata = obj.metadata