decoder/{dsdiff,dsf,mpg123,wavpack}: avoid exceptions in scan methods

The scan methods must be "noexcept".

src/decoder/plugins/DsfDecoderPlugin.cxx

@@ -334,14 +334,14 @@ dsf_scan_stream(InputStream &is,
 	if (!dsf_read_metadata(nullptr, is, &metadata))
 		return false;
 
-	auto audio_format = CheckAudioFormat(metadata.sample_rate / 8,
-					     SampleFormat::DSD,
-					     metadata.channels);
+	const auto sample_rate = metadata.sample_rate / 8;
+	if (!audio_valid_sample_rate(sample_rate))
+		return false;
 
 	/* calculate song time and add as tag */
 	const auto n_blocks = metadata.n_blocks;
 	auto songtime = SongTime::FromScale<uint64_t>(n_blocks * DSF_BLOCK_SIZE,
-						      audio_format.sample_rate);
+						      sample_rate);
 	tag_handler_invoke_duration(handler, handler_ctx, songtime);
 
 #ifdef ENABLE_ID3TAG