Fixed runtimeException in launchbackup

In reference to this thread on the forums: http://forums.zpanelcp.com/Thread-SOLVED-Launch-Backup-No-Longer-Working?pid=85265

I ran into an issue where launching a manual backup suddenly stopped working (wouldn't calculate the current public directory size) after uploading lots of site files. Looking into it further I found that $file->getSize would throw a RuntimeException if it didn't have permission to read the size of a file.