Fix Issue 12114 - buildNormalizedPath returns null instead of "."

[Issue details](https://issues.dlang.org/show_bug.cgi?id=12114)

in short:
`buildNormalizedPath(".")` and `buildNormalizedPath("foo", "..")` should both return `.` instead of null
Sorry, I missed this the first time. The other uses of ```==``` in this file have whitespace. This should too.