- Checking for null bytes is unnecessary because the check for illegal
characters directly below it will catch them.
- We can use the path.extname method to get the file extension more
cleanly. It returns the *last* extension (e.g.
path.extname('file.foo.js') === '.js'), so behavior is preserved.
- Normalizing the path is unnecessary. We don't allow any path
separators in the file name, so it does nothing.
- Stripping '..', path separators, and '$' is unnecessary because of the
earlier illegal character check.
