crashtesting: empty brace init of o3tl::enumarray doesn't zero each element

crashtesting: empty brace init of o3tl::enumarray doesn't zero each element

so the stretch used to layout fdo66401-6.docx is random, leading to
sometimes too much stretch for cairo/freetype to handle and the
conversion crashes. A problem since:

commit d51db77c8d87f210785a8a8c6dd875f7bacddb3c
Date:   Tue Oct 15 01:57:12 2019 +0300

    Remove some memset calls

    Replace them with default initialization or calloc

Change-Id: I49408eee6c7e36bd9c98cbb10c7f95a57c0f7a11
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/138876
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>