bug#43374: 26.1: read-directory-name not respecting MUST-MATCH arg

[Boruch Baum]

based upon the function's docstring, I was expecting the following to
return nil for a non-existing directory. Instead, it returns a string of
the non-existing directory.

   (read-directory-name "Directory: " nil nil t nil)



--
hkp://keys.gnupg.net
CA45 09B5 5351 7C11 A9D1  7286 0036 9E45 1595 8BC0