Add Magnet dialog retains download directory from previous server

Version: 512b63c

Steps to reproduce

1. Select the Server 1 tab.
2. Open the Add Magnet dialog.
3. Paste multiple magnet links, one per line (This is how I reproduced it; it is unclear whether multiple links are required or merely make the issue easier to trigger.)
4. Click Add.
5. Immediately switch to the Server 2 tab.
6. Open the Add Magnet dialog.

Actual behavior

The download directory field and its saved-directory list may still contain Server 1 paths.

If the torrent is added without noticing this, Server 2 can receive a path that does not exist on that server. This can cause an immediate path error or a failure when Transmission tries to move the completed download from its incomplete directory.

Expected behavior

The download directory should always be refreshed for the currently selected server. Paths from one server must never be reused for another server.

Reproducibility

It happened both times when I added the same set of magnets to two different servers.

It may require actually starting a multi-link addition before switching servers. I do not remember encountering it before multi-line magnet support was introduced.

Locate the Add Magnet dialog and the server-tab change handling, then reproduce the issue by adding magnets on Server 1 before switching to Server 2. Verify the download directory and saved-directory list refresh for the selected server and that paths from the previous server are not reused.