sw: call SwEditShell::CalcLayout to avoid crashes

(i.e. similar to 83c0018dba00ae0c0cf5b179cfc7a47ce08ff2b7 on master)

Change-Id: Ia24c7cadd382b89d43bc2e1081ef85751cb6eca6
Reviewed-on: https://gerrit.libreoffice.org/9262
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>