VirtualDirectorySelectorDlg: Improve the 'New VD' suggestion code

    There were 2 problems with the previous code:
      The suggestion, if accepted, would be appended to the current path. So if someone accepted foo:bar:baz, that's exactly what was appended, even if the current selection was foo:bar, resulting in foo:bar:foo:bar:baz.
      The new VD wasn't selected afterwards, because VirtualDirectorySelectorDlg::SelectPath was thoroughly broken.