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
Why the extra spaces before `return`? It should either be 1 space following the condition, or it should be on a new line, indented.