rendering svg causes int overflows in blend_vertical_gradient_argb

1. Have a build of Qt configured with "-sanitize undefined".
2. Build the attached project with that.
3. Run the resulting binary with the attached svg file as parameter.
   The sanitizer will show overflows:

   /home/qtrob/dev/src/qt-dev_12.21-base_imageformats_svg/qtbase/src/gui/painting/qdrawhelper.cpp:4993:19: runtime error: 6,4521e+09 is outside the range of representable values of type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/src/qt-dev_12.21-base_imageformats_svg/qtbase/src/gui/painting/qdrawhelper.cpp:4993:19 in 
   /home/qtrob/dev/src/qt-dev_12.21-base_imageformats_svg/qtbase/src/gui/painting/qdrawhelper.cpp:5001:59: runtime error: signed integer overflow: -27763137 * 232 cannot be represented in type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/src/qt-dev_12.21-base_imageformats_svg/qtbase/src/gui/painting/qdrawhelper.cpp:5001:59 in 
   /home/qtrob/dev/src/qt-dev_12.21-base_imageformats_svg/qtbase/src/gui/painting/qdrawhelper.cpp:5001:63: runtime error: signed integer overflow: -2146080488 + -2147483648 cannot be represented in type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/src/qt-dev_12.21-base_imageformats_svg/qtbase/src/gui/painting/qdrawhelper.cpp:5001:63 i
   

Google's oss-fuzz found this as issue 63392. Their report is public. It went to "Verified" state in November but I can still reproduce the issue with Qt's latest sources.