Fix the project existence check

muhoo on IRC was asking about an issue with the library where it was thinking there was a project.clj when there actually wasn't. I took a look and the fix was easy. He confirmed it works.

Regarding the fix, I really wanted to swap the if branches so that I didn't have to use if-not, but that would have messed up your comment and I didn't want to remove it.

Cheers!