Bugfix: check that the error is not a FileNotFound (ENOENT) error

Hello there,

we encounter a bug for some months now, in our tests. We tracked down the issue and found a bug in chokidar. To make a long story short, chokidar issues an *fs.realpath*, and ignore the result if there is a ENOENT error. Then it issues a *fs.stat* call, but take for granted that the file hasn't been removed in the interval, which is obviously false under certain workloads.

Hope you'll like it.