Section download count is recalculated when re-enable section download

How to reproduce:

1. Enable section downloads.
2. Start downloading a section that has several modules to download.
3. When some modules have been downloaded and some are still in progress, disable the download and enable it again.
4. Check that the number of downloaded goes back to 0 and the total is now the number of pending downloads. E.g. 5/10 -> 0/5.