Qbittorrent: [Bug] Can't remove URL for web seed/HTTP source

[coolio2013]

Please provide the following information

qBittorrent version and Operating System

v4.1.6 official, Win-32

### If on linux, libtorrent and Qt version
-

What is the problem

Some .torrents provide URLs for leeching.
Issue is: 'Remove Web seed' is not working in 'HTTP Sources' of that torrent.
The URL disappears from the UI and from .fastresume-file, but is not removed from the .torrent-file. So qbt tries to download from that URL again after restart of qbt.

Background: If the URL from the .torrent is not reachable, these messages floods the LOG, up to twice a second. If LOG is enabled in the UI (for showing), this will eventually block qbt for 2 minutes on my system.

What is the expected behavior

Delete the URL from the .torrent-file.

Steps to reproduce

Sorry, currently can't provide a .torrent-file.

Extra info(if any)

a. Please backport to 4.1.x, if possible.
b. Could not find any other issue like this on github, crawling 13 pages. Sorry, if it is a dupe.

[Chocobo1]

I confirm this on libtorrent RC_1_2 bd0d01153641ffb1913f531b68c860b90efe0735
And also RC_1_1 84f10d05caff0d20213280951752797d166e1759

@arvidn
I suspect this is a bug in libtorrent.
We currently use read_resume_data() to read in the fastresume and it seems that the fastresume isn't getting priority here, that is, if there is no url-list field in fastresume then there should be no web seed for the torrent.

[glassez]

there is no url-list field in fastresume then there should be no web seed for the torrent.

It's expected behavior, IMO.

[Chocobo1]

Will be fixed in upcoming v4.2.0. (PR #11104)