Log messages in FileLink$FileLinkInputStream#tryOpen are reversed

The log message in `tryOpen` is reversed:

            if (currentPath != null) {
              LOG.debug("link open path=" + path);
            } else {
              LOG.trace("link switch from path=" + currentPath + " to path=" + path);
            }

By reading the logic, we can see that when switching paths (currentPath != null) it will log that it opened a path, and when opening a path, it will print that it switched from path=null to the new path.