Silence the glibc compile warning and actually handle a wrong
return value.

Change-Id: Icdbc8e655d4b8ad20699dfd0abdbf3405a49f898
(cherry picked from commit e4a3bf06)
Reviewed-on: https://gerrit.libreoffice.org/18034Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>