tdf#159213 a11y: Only send child event if there's a child

When reviewing all the places sending an `AccessibleEventId::CHILD`
event as described in tdf#159213 comment 8, this here looks
like one where the child might not be set.
Add a corresponding check to avoid sending an invalid event.

Change-Id: I6fea72e8a0619eeec7ac7c9d38dec996ab34752f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/163427
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

0 files changed, 0 insertions, 0 deletions