-1 is the default value for QSurfaceFormat::alphaBufferSize. Changing it
to 0 may result an unexpected pixel format change by ARB OpenGL
extension.
Fixes: QTBUG-107629
Change-Id: Ia6a1b90fba6c43b6872b406f4fd946d937135cf8
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
(cherry picked from commit 600752aa972d1e46792e18f1ec6dd0b519722e65)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>