Running beep.rs example with ALSA only loads data to buffer once about cpal

[nchashch]

I tried to debug this problem and I have found that libc::poll call in EventLoop::run method in src/alsa/mod.rs at L258 doesn't return (it seems it just runs in an infinite loop) after a few iterations (hence a short bit of sound plays at the begining).

Also on my machine Buffer::finish method (defined at L674 in src/alsa/mod.rs) is called only once or twice (so alsa::snd_pcm_writei is called only once or twice) after that SamplesStream::schedule is called (maybe something goes wrong there) and then Buffer::finish is never called again.

[jwestfall69]

Can you guys verify the above patch fixes the beep stall.

I'm a little unsatisfied with the patch with where I'm calling alsa::snd_pcm_sw_params_set_avail_min(),. Its inside the bits that are setting up buffer_len/period_len values, which seems like bad form.

[tomaka]

@jwestfall69 The style is not a problem for me.