Add torrent or magnet popup's tab order

[bluenlive]

Hello. Thank you for the good program.

When the "Add Torrent" popup appears, the tab is not positioned on the "Add" button. So, if you select a torrent with the keyboard, you have to move it to the "Add" button. (Shift-Tab twice, maybe)

It looks like a fix to move the initial position of the tab to "Add" is needed.