audiounit_ios: Fill the remainder of the buffer with zeros

If we didn't have enough data to fill the buffer, fill the rest
of it with zeros. This is better than playing back whatever happened
to be there from before.
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

modules/audio_output/audiounit_ios.c

@@ -389,6 +389,8 @@ static OSStatus RenderCallback(vlc_object_t *p_obj,
         memcpy(targetBuffer, buffer, __MIN(bytesToCopy, availableBytes));
         TPCircularBufferConsume(&p_sys->circular_buffer, __MIN(bytesToCopy, availableBytes));
         VLC_UNUSED(inNumberFrames);
+        if (availableBytes < bytesToCopy)
+            memset((uint8_t*) targetBuffer + availableBytes, 0, bytesToCopy - availableBytes);
     }
 
     return noErr;