When a wrong temp directory was set (e.g. wrong path in xcu ist set),
you get a assert in the LO-Debug Version, this patch avoid this assertion.

Change-Id: I192f682860ad9cddf907e4b239eff36b4bd6072d
Reviewed-on: https://gerrit.libreoffice.org/46846Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>