input/InputStream: ReadTag() returns std::unique_ptr<Tag>

src/input/IcyInputStream.hxx

@@ -63,7 +63,7 @@ public:
 
 	/* virtual methods from InputStream */
 	void Update() override;
-	Tag *ReadTag() override;
+	std::unique_ptr<Tag> ReadTag() override;
 	size_t Read(void *ptr, size_t size) override;
 };