Fix invalid init buffer length in zlog_msg_ex

Author: bukka

sapi/fpm/fpm/zlog.c

@@ -249,7 +249,7 @@ void zlog_msg_ex(const char *function, int line, int flags,
 	size_t prefix_len = strlen(prefix);
 	size_t msg_len = strlen(msg);
 
-	zlog_stream_init_for_msg(&stream, ZLOG_NOTICE, prefix_len + prefix_len);
+	zlog_stream_init_for_msg(&stream, ZLOG_NOTICE, msg_len + prefix_len);
 	zlog_stream_prefix_ex(&stream, function, line);
 	zlog_stream_str(&stream, prefix, prefix_len);
 	zlog_stream_str(&stream, msg, msg_len);