flac: don't overwrite bitspersample

The decoder might have filters in place that cause it to output to
something else than s16n

Close: #6400

modules/codec/flac.c

@@ -233,6 +233,7 @@ static void DecoderMetadataCallback( const FLAC__StreamDecoder *decoder,
     p_dec->fmt_out.audio.i_physical_channels =
         p_dec->fmt_out.audio.i_original_channels =
             pi_channels_maps[metadata->data.stream_info.channels];
+    if (!p_dec->fmt_out.audio.i_bitspersample)
         p_dec->fmt_out.audio.i_bitspersample =
             metadata->data.stream_info.bits_per_sample;