Fixes regression introduced in b4981f9d4c,
due to which it was possible to back-tab into a widget even though it or
its focusProxy had a NoFocus policy.
As a drive-by, split the complicated if-statement up a bit for improved
readability.
Change-Id: Ib0ac2604076e812e340b11534c23ae8ae958d082
Fixes: QTBUG-76924
Pick-to: 5.15 5.12
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
0dbd2dd863