decoder/flac: throw exception on FLAC__stream_decoder_new() failure

src/decoder/plugins/FlacDecoderPlugin.cxx

@@ -120,12 +120,6 @@ static FlacStreamDecoder
 flac_decoder_new(void)
 {
 	FlacStreamDecoder sd;
-	if (!sd) {
-		LogError(flac_domain,
-			 "FLAC__stream_decoder_new() failed");
-		return sd;
-	}
-
 	if(!FLAC__stream_decoder_set_metadata_respond(sd.get(), FLAC__METADATA_TYPE_VORBIS_COMMENT))
 		LogDebug(flac_domain,
 			 "FLAC__stream_decoder_set_metadata_respond() has failed");

src/decoder/plugins/FlacStreamDecoder.hxx

@@ -25,6 +25,7 @@
 #include <FLAC/stream_decoder.h>
 
 #include <utility>
+#include <stdexcept>
 
 #include <assert.h>
 
@@ -36,7 +37,10 @@ class FlacStreamDecoder {
 
 public:
 	FlacStreamDecoder()
-		:decoder(FLAC__stream_decoder_new()) {}
+		:decoder(FLAC__stream_decoder_new()) {
+		if (decoder == nullptr)
+			throw std::runtime_error("FLAC__stream_decoder_new() failed");
+	}
 
 	FlacStreamDecoder(FlacStreamDecoder &&src)
 		:decoder(src.decoder) {