fix: check that sounds are loaded in seek (returning current position)

[rigobauer]

If sounds are not loaded and calls .seek() you get this error:

Cannot read property '_id' of undefined

[jzstern]

It also appears the play event is being triggered before the song is loaded. What's the recommended way for determining progress and continually updating it?

track.on("play", () => {
    const duration = track.duration()

    setProgressUpdater(setInterval(() => {
        try {
            let elapsed = track.seek()
            let progress = elapsed / duration
            setTimeElapsed(elapsed)
            setProgress(progress.toFixed(4))
        } catch (e) {
            // TODO - fix this
            console.error(e)
        }
    }, 200))
})
})