mpd: Update to 0.19.11, fix gcc5 builds

Add a patch from the Alpine Linux project to fix a musl build issue with gcc 5:

Signed-off-by: Ted Hess <thess@kitschensync.net>

sound/mpd/patches/220-handle_slow_server_stream_startup.patch

@@ -1,6 +1,6 @@
 --- a/src/decoder/plugins/FfmpegDecoderPlugin.cxx
 +++ b/src/decoder/plugins/FfmpegDecoderPlugin.cxx
-@@ -458,6 +458,13 @@ ffmpeg_probe(Decoder *decoder, InputStre
+@@ -467,6 +467,13 @@ ffmpeg_probe(Decoder *decoder, InputStre
  
  	unsigned char buffer[BUFFER_SIZE];
  	size_t nbytes = decoder_read(decoder, is, buffer, BUFFER_SIZE);