Retry failed preloads

[derat]

The web player seems to get stuck if it fails to preload a track due to e.g. a network hiccup:

Preloading 5745869450117120 (...)
song:1 Failed to load resource: net::ERR_INTERNET_DISCONNECTED
music-player.js:642 Starting preloaded 5745869450117120 (...)
music-player.js:941 Scaling amplitude by 0.404
music-player.js:662 Playing
.../:1 Uncaught (in promise) DOMException: The element has no supported sources.

Clicking the play button didn't reload the track, but clicking prev and then next worked.

Maybe I can catch the error and retry? Hopefully it's possible to repro this by disabling wifi just before preloading and then enabling it after it fails.