Add a check that the reference we create the TestAXObject object from is
valid, and assert that it is before calling properties. Verify that the
rows we get all have the correct number of children (the columns) before
trying to read the cell values.
As a drive-by, change the relevant code to use property syntax, and
release objects consistently.
Task-number: QTBUG-122751
Change-Id: I1db3e4446c569235cfc0f3092adc7369ad826368
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit dac1a338d31be82004f0f2666105ad18e557409b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
39524fabc4