...introduced with 26be5f21 "unotools: don't go
belly-up if temp dir is wrong or empty".  At least Flatpak builds can create a
/not/found/dir directory just fine.

Change-Id: I73115ac99498ac584be77153ef66bba3036392c3
Reviewed-on: https://gerrit.libreoffice.org/47267Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>