avdevice/alsa: wait until playback buffers are drained before closing

This fixes early abort on ALSA playback
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavdevice/alsa.c

@@ -300,6 +300,8 @@ av_cold int ff_alsa_close(AVFormatContext *s1)
 {
     AlsaData *s = s1->priv_data;
 
+    snd_pcm_nonblock(s->h, 0);
+    snd_pcm_drain(s->h);
     av_freep(&s->reorder_buf);
     if (CONFIG_ALSA_INDEV)
         ff_timefilter_destroy(s->timefilter);