Hi,
There is some problem with your file, I've checked it and correctly the line is like this:
if ($title = JoomSEF::_getCustomMenuTitle($option)) {
There's only one "=" character, not two of them, so the $title variable gets defined and is checked right away. Are you sure you haven't made any custom modifications in the file? What is the exact version of JoomSEF you're using (3.8.x)?