memory will leaks

the payload pointor assigned two memory,will lead to memory leaks

@@ -664,7 +664,7 @@ int SrsSource::on_meta_data(SrsCommonMessage* msg, SrsOnMetaDataPacket* metadata
 	}
 	srs_verbose("get metadata size success.");
 	
-	char* payload = new char[size];
+	char* payload = NULL;
 	memset(payload, 0, size);
 	if ((ret = metadata->encode(size, payload)) != ERROR_SUCCESS) {
 		srs_error("encode metadata error. ret=%d", ret);