vcl-quartz: fix for fdo#77993 (specific to OS X <10.6)

When using current method, early version of CoreText crashes internally.

Change-Id: Id451d72ac26e4777b61f5d3fec6d4b046c46a749
Reviewed-on: https://gerrit.libreoffice.org/9180
Tested-by: David Tardon <dtardon@redhat.com>
Reviewed-by: David Tardon <dtardon@redhat.com>