Commit 8010e906d3 accidentally ended up
removing the removal-on-undefined-insertion check by calling insertAt
instead of insert, which had it. This patch moves the check back into
setValueAt.
Change-Id: Ic381e284d3da37e31c4eb29f79dfab9c55c2e3e9
Fixes: QTBUG-77204
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>