Don't panic if a write doesn't fully complete

[thenickdude]

On my Raspberry Pi 3B+, after about 5-10 mins of piping different files to the speaker, I get an error like:

Error: write() failed: 3192

But it's perfectly reasonable for a write() to write fewer bytes than requested (e.g. if the audio device's buffer fills up), so this PR fixes the code so it doesn't panic in this situation and just retries the write of the remaining bytes.

Now my Pi plays flawlessly.

[Leone25]

I'd like to add to this because I'm having similar issues. I've tried the modified branch and it doesn't seem to fix the issue for me, is still get the following error

Error: write() failed: 0

I'm confused as to why it is needed to error. As a quick test I've modified the following

207c207
< done(new Error(`write() failed: ${r}`))
> done()

and now my code works just fine without crashing the whole app, can't we just ignore length 0 or prevent it from getting to line 207 elsewhere?

thx,
Rico