Removing entries in audio compilation doesn't always clear their timing from progress bar

Steps

1. start audio composition
2. add 4 audio files
3. select various tracks and drag them around a few times
4. entries will be duplicated rather than moved (issue #35 (closed))
5. delete one entry at a time until there are no more left
6. notice that progress isn't clear

Tested on Xubuntu 20.04 with Xfce 0.6.2.