input/Plugin: migrate open() from class Error to C++ exceptions

src/input/InputStream.hxx

@@ -115,16 +115,17 @@ public:
 	 * Opens a new input stream.  You may not access it until the "ready"
 	 * flag is set.
 	 *
+	 * Throws std::runtime_error on error.
+	 *
 	 * @param mutex a mutex that is used to protect this object; must be
 	 * locked before calling any of the public methods
 	 * @param cond a cond that gets signalled when the state of
 	 * this object changes; may be nullptr if the caller doesn't want to get
 	 * notifications
-	 * @return an #InputStream object on success, nullptr on error
+	 * @return an #InputStream object on success
 	 */
 	gcc_nonnull_all
-	static InputStreamPtr Open(const char *uri, Mutex &mutex, Cond &cond,
-				   Error &error);
+	static InputStreamPtr Open(const char *uri, Mutex &mutex, Cond &cond);
 
 	/**
 	 * Just like Open(), but waits for the stream to become ready.
@@ -132,8 +133,7 @@ public:
 	 */
 	gcc_nonnull_all
 	static InputStreamPtr OpenReady(const char *uri,
-					Mutex &mutex, Cond &cond,
-					Error &error);
+					Mutex &mutex, Cond &cond);
 
 	/**
 	 * The absolute URI which was used to open this stream.