PictureFlow: Fix playback behavior after appending

- Once items have been appended, the existing playlist can
not be reused when selecting an album for regular
playback, since the playlist will be out of sync with the
album's track list

- Don't re-shuffle playlist after appending items

Change-Id: I3b6035033ad1d59f9916c711f13737bb0987c4f6

apps/plugins/pictureflow/pictureflow.c

@@ -3529,7 +3529,7 @@ static void start_playback(bool append)
     else
         return;
 
-    if (rb->global_settings->playlist_shuffle)
+    if (!append && rb->global_settings->playlist_shuffle)
         position = rb->playlist_shuffle(*rb->current_tick, pf_tracks.sel);
 play:
     /* TODO: can we adjust selected_track if !play_selected ?
@@ -3540,8 +3540,10 @@ play:
         rb->playlist_start(position, 0, 0);
         /* make warn on playlist erase work */
         rb->playlist_get_current()->num_inserted_tracks = 0;
+        old_playlist = center_slide.slide_index;
     }
-    old_playlist = center_slide.slide_index;
+    else
+        old_playlist = -1;
     old_shuffle = shuffle;
 }
 #endif