Retrieves the current selection from the list box of a combo box.
It assumes that the list box has been filled by the DlgDirListComboBox member function and that the selection is a drive letter, a file, or a directory name.
The DlgDirSelectComboBox member function copies the selection to the specified buffer. If there is no selection, the contents of the buffer are not changed.
It does not allow more than one filename to be returned from a combo box.