QHighDpiScaling: fix potential null pointer dereference

It's not guaranteed that QPlatformScreen::screen should always return a
valid pointer. Furthermore, you can run into this situation with, for
example, two screens setup.

Task-number: QTBUG-53022
Change-Id: Ic23bb2c30b1245f98a793a44cc5e0b39f9afac4b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gui/kernel/qhighdpiscaling.cpp b/src/gui/kernel/qhighdpiscaling.cpp
index 76548d5d86..704dcee633 100644
--- a/src/gui/kernel/qhighdpiscaling.cpp
+++ b/src/gui/kernel/qhighdpiscaling.cpp
@@ -657,7 +657,8 @@ qreal QHighDpiScaling::screenSubfactor(const QPlatformScreen *screen)
         // Check if there is a factor set on the screen object or associated
         // with the screen name. These are mutually exclusive, so checking
         // order is not significant.
-        QVariant byIndex = screen->screen()->property(scaleFactorProperty);
+        auto qScreen = screen->screen();
+        auto byIndex = qScreen ? qScreen->property(scaleFactorProperty) : QVariant();
         auto byNameIt = qNamedScreenScaleFactors()->constFind(screen->name());
         if (byIndex.isValid()) {
             screenPropertyUsed = true;