test: add a test case for the path.posix.resolve

In posix path.resolve should handle relative paths to be safe even if process.cwd fails.

At lib/path.js#999:

    return resolvedPath.length > 0 ? resolvedPath : '.';

Else branch wasn't covered.

Add a test case to cover this.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines