pcm_utils: check pcm_convert()==0

It is illegal to pass an empty audio buffer around.  pcm_resample()
sometimes seems to result in 0 samples, maybe related to
libsamplerate.  To work around that problem, add special checks after
both pcm_convert() invocations.  Removed the pcm_resample()==0 checks
from pcm_convert().

src/decoder_api.c

@@ -249,6 +249,13 @@ decoder_data(struct decoder *decoder,
 		length = pcm_convert(&dc.in_audio_format, _data,
 				     length, &dc.out_audio_format,
 				     data, &decoder->conv_state);
+
+		/* under certain circumstances, pcm_convert() may
+		   return an empty buffer - this condition should be
+		   investigated further, but for now, do this check as
+		   a workaround: */
+		if (length == 0)
+			return DECODE_COMMAND_NONE;
 	}
 
 	if (replay_gain_info != NULL && (replay_gain_mode != REPLAY_GAIN_OFF))

src/output_thread.c

@@ -69,9 +69,17 @@ static void ao_play(struct audio_output *ao)
 
 	assert(size > 0);
 
-	if (!audio_format_equals(&ao->inAudioFormat, &ao->outAudioFormat))
+	if (!audio_format_equals(&ao->inAudioFormat, &ao->outAudioFormat)) {
 		convertAudioFormat(ao, &data, &size);
 
+		/* under certain circumstances, pcm_convert() may
+		   return an empty buffer - this condition should be
+		   investigated further, but for now, do this check as
+		   a workaround: */
+		if (size == 0)
+			return;
+	}
+
 	ret = ao->plugin->play(ao->data, data, size);
 	if (!ret) {
 		ao->plugin->cancel(ao->data);

src/pcm_utils.c

@@ -379,8 +379,6 @@ pcm_convert_16(const struct audio_format *src_format,
 				      dest_format->sample_rate,
 				      dest_buffer, dest_size,
 				      &state->resample);
-		if (len == 0)
-			exit(EXIT_FAILURE);
 	}
 
 	return len;
@@ -421,8 +419,6 @@ pcm_convert_24(const struct audio_format *src_format,
 				      dest_format->sample_rate,
 				      (int32_t*)dest_buffer, dest_size,
 				      &state->resample);
-		if (len == 0)
-			exit(EXIT_FAILURE);
 	}
 
 	return len;