Resolves: rhbz#1104068 crash converting fontwork to curve

via metafile, i.e. take fontwork example 11, convert
to metafile and convert that to curve

was coverity#1019335 Dereference after null check

(cherry picked from commit d77cc9d2cdc702f2b2016498df107f4120d27690)

Change-Id: I309e0c3f8a0630991e2aad64f995567e0920be3b
Reviewed-on: https://gerrit.libreoffice.org/9649
Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>