For whatever reason oox shape import code uses OUStrings that contain
'\0' characters.

The rtl_uString / rtl_String are allowed to contain '\0' but the
strncmp/wcsncmp functions stop comparing on the first '\0', so use
memcmp/wmemcmp instead.

(regression from 28198900)

Change-Id: If148927f19d065a21f32f3c14433b0bda7ae9301
Reviewed-on: https://gerrit.libreoffice.org/29384Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>