ao_alsa: reinitialize if device got broken

Apparently, physically disconnecting the audio device (consider USB
audio) breaks the ALSA device handle forever. It will signal ENODEV.
Fortunately, it's easy for us to handle this, and we can just use
existing mechanisms that will make the playback core close and reopen
the AO. Whether the immediate reopening will actually succeeds really is
ALSA's problem, though.

audio/out/ao_alsa.c

@@ -846,6 +846,9 @@ static int play(struct ao *ao, void **data, int samples, int flags)
 
         if (res == -EINTR || res == -EAGAIN) { /* retry */
             res = 0;
+        } else if (res == -ENODEV) {
+            MP_WARN(ao, "Device lost, trying to recover...\n");
+            ao_request_reload(ao);
         } else if (res < 0) {
             if (res == -ESTRPIPE) {  /* suspend */
                 resume_device(ao);