encoder: migrate from class Error to C++ exceptions

src/encoder/plugins/OggEncoder.hxx

@@ -47,9 +47,8 @@ public:
 	}
 
 	/* virtual methods from class Encoder */
-	bool Flush(Error &) override {
-		Flush();
-		return true;
+	void Flush() final {
+		flush = true;
 	}
 
 	size_t Read(void *dest, size_t length) override {
@@ -67,11 +66,6 @@ public:
 
 		return ReadPage(page, dest, length);
 	}
-
-protected:
-	void Flush() {
-		flush = true;
-	}
 };
 
 #endif