Small "hack" to make AutoUpdater download from custom url

[Maxetto]

Not the best approach, but as long as you have set the correct custom url for download updates and it points directly to a file it will make the new autoupdater introduced in 1.4.0 download the correct version.

Previously it would download the official unmodified version, breaking the custom values the client had.

A proper way would be to use a patch file, but I have no idea how >.<

[bryangerlach]

Does this not work on linux or android? I haven't look into it at all. Does this change how the client checks for updates, or is it still checking based on official rustdesk versions?

[Maxetto]

For now it seems only Windows and MacOS have this feature. Android I can confirm it still open a webpage with the url you set, Linux I don't know.
The PR that added the feature was that: rustdesk/rustdesk#11618

It only changes the download url, all the update check logic still follows the official rustdesk versions.

[Maxetto]

https://github.com/rustdesk/rustdesk/blob/965cb704ecc7fcb408416949e9e68bba646d43d2/flutter/lib/desktop/widgets/update_progress.dart#L24
downloadUrl = '$downloadUrl/$downloadFile';

Actually maybe it could work by just replacing this line instead of messing with many lines of flutter_ffi.rs 🤔