rather than check if it exists, and then get it if it exists

I wonder if the else branch from...

commit 0c2229dc
Date:   Fri Mar 24 13:04:32 2017 +0100

    tdf#58624 sw: fix ~SwAccessibleContext() use-after-free race

is still relevant after this

Change-Id: Idabea01f0c450b07b75214c5a83460e1d0319802
Reviewed-on: https://gerrit.libreoffice.org/54904Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>