Fix load queue seeking

[mahmed2000]

Mpv requires the file's sample table to be loaded before any seek commands are considered valid. IsSongLoaded was insufficient since mpv stops being idle before the file is ready, and before mpv allows seek commands to work. The original plan was to wait on the "file-loaded" event, but turns out mpv has the seekable property, which makes this trivial.

This checks if mpv has entered a seekable state every 100ms. The error still needs to be logged and handled since it can loop infinitely.

See #71 (comment) for context.

[xxxserxxx]

Reviewed and merged onto branch xxxserxxx

This should enable loading a saved queue and seeking to the last saved point, ĉu ne?

[mahmed2000]

As far as I've tested, yes. The seeking for queue-loading on "l" works correctly with this change now.

To be clear, the existing implementation already had the seek call, all that was needed was to make it wait for the a-OK from mpv before trying.

What I haven't tested is if mpv gets a garbled link or anything else renders it in a state where it never enters a seekable state but keeps the file loaded. And if the user presses "l" multiple times in quick succession. Its all on a separate go-routine so it shouldn't matter too much, but still something to consider.

[xxxserxxx]

Hmm. I added the queue loading and saving, and I know I fussed a lot with the seeking before I gave up on it. I'm a little surprised that I left it in a state where it works properly, but I'm not going to look a gift horse in the mouth.

As I mentioned, your PR is merged into the xxxserxxx branch.