Adjust minimum alternative rate limits to zero

[FurkanKambay]

I don't know if there was a reason for not having 0 as an option (for 0 B/s, not unlimited). If it's allowed, there you go.
edit: ignore this. didn't realize that 0 was used by libtorrent as unlimited. can't achieve this by allowing 0.

[sledgehammer999]

upload_rate_limit and download_rate_limit sets the session-global limits of upload and download rate limits, in bytes per second. By default peers on the local network are not rate limited.

A value of 0 means unlimited.

The "unlimited" setting is controlled by the checkbox that exists in the side of the spinbox.

[FurkanKambay]

@sledgehammer999 sorry, should've mentioned this. I meant 0 to be off, not unlimited.
Can we use -1 for 0B/s since it's signed int?

edit: Sorry, just realized it's a libtorrent thing. Also, I admit that I opened the PR immaturely. Anyway, I'd like to ask, if turning off were implemented, would it be accepted?

[sledgehammer999]

Setting speed to 0 B/s effectively means stopping transfer. So the correct method is to either stop the respective torrent or stop the entire session ( <--- a libtorrent::session )

[FurkanKambay]

@sledgehammer999 Yeah, stopping the current session is probably good. I won't work on this separately since it's going to be included in #9203 if I can finish it. Thanks.