pcm/PcmConvert: eliminate Open() and Close()

Let the constructor and destructor do this.  This means that all users
have to be converted to allocate PcmConvert dynamically.

src/decoder/Bridge.cxx

@@ -37,15 +37,16 @@
 #include <string.h>
 #include <math.h>
 
+DecoderBridge::DecoderBridge(DecoderControl &_dc, bool _initial_seek_pending,
+			     std::unique_ptr<Tag> _tag) noexcept
+	:dc(_dc),
+	 initial_seek_pending(_initial_seek_pending),
+	 song_tag(std::move(_tag)) {}
+
 DecoderBridge::~DecoderBridge()
 {
 	/* caller must flush the chunk */
 	assert(current_chunk == nullptr);
-
-	if (convert != nullptr) {
-		convert->Close();
-		delete convert;
-	}
 }
 
 bool
@@ -255,11 +256,9 @@ DecoderBridge::Ready(const AudioFormat audio_format,
 		FormatDebug(decoder_domain, "converting to %s",
 			    ToString(dc.out_audio_format).c_str());
 
-		convert = new PcmConvert();
-
 		try {
-			convert->Open(dc.in_audio_format,
-					      dc.out_audio_format);
+			convert = std::make_unique<PcmConvert>(dc.in_audio_format,
+							       dc.out_audio_format);
 		} catch (...) {
 			error = std::current_exception();
 		}

src/decoder/Bridge.hxx

@@ -44,7 +44,7 @@ public:
 	 * For converting input data to the configured audio format.
 	 * nullptr means no conversion necessary.
 	 */
-	PcmConvert *convert = nullptr;
+	std::unique_ptr<PcmConvert> convert;
 
 	/**
 	 * The time stamp of the next data chunk, in seconds.
@@ -107,10 +107,7 @@ public:
 	std::exception_ptr error;
 
 	DecoderBridge(DecoderControl &_dc, bool _initial_seek_pending,
-		      std::unique_ptr<Tag> _tag)
-		:dc(_dc),
-		 initial_seek_pending(_initial_seek_pending),
-		 song_tag(std::move(_tag)) {}
+		      std::unique_ptr<Tag> _tag) noexcept;
 
 	~DecoderBridge();