[REG 6.2.2 -> 6.2.3] Integer overflow when rendering svg image

1. Have a build of Qt including qtsvg configured with "-sanitize undefined".
2. Use that to build the attached project.

   qt-cmake /tmp/report/ && cmake --build .
   

3. Run the resulting program and pass the input file.

   ./report /tmp/report/43998.svg
   

   You will see output like:

   /home/qtrob/dev/clang-10.0.0/qt-dev_01.10-base_svg-fubsan/qtbase/include/QtCore/../../../../../src/qt-dev_01.10-base_svg/qtbase/src/corelib/kernel/qmath.h:81:16: runtime error: -nan is outside the range of representable values of type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/clang-10.0.0/qt-dev_01.10-base_svg-fubsan/qtbase/include/QtCore/../../../../../src/qt-dev_01.10-base_svg/qtbase/src/corelib/kernel/qmath.h:81:16 in 
   /home/qtrob/dev/clang-10.0.0/qt-dev_01.10-base_svg-fubsan/qtbase/include/QtCore/../../../../../src/qt-dev_01.10-base_svg/qtbase/src/corelib/kernel/qmath.h:75:16: runtime error: -nan is outside the range of representable values of type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/clang-10.0.0/qt-dev_01.10-base_svg-fubsan/qtbase/include/QtCore/../../../../../src/qt-dev_01.10-base_svg/qtbase/src/corelib/kernel/qmath.h:75:16 in 
   /home/qtrob/dev/src/qt-dev_01.10-base_svg/qtbase/src/corelib/tools/qrect.h:183:46: runtime error: signed integer overflow: -2147483648 - 1 cannot be represented in type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/src/qt-dev_01.10-base_svg/qtbase/src/corelib/tools/qrect.h:183:46 in 
   /home/qtrob/dev/src/qt-dev_01.10-base_svg/qtbase/src/corelib/tools/qrect.h:183:70: runtime error: signed integer overflow: -2147483648 - 1 cannot be represented in type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/src/qt-dev_01.10-base_svg/qtbase/src/corelib/tools/qrect.h:183:70 in 
   /home/qtrob/dev/src/qt-dev_01.10-base_svg/qtbase/src/gui/kernel/../../corelib/global/qglobal.h:790:14: runtime error: -nan is outside the range of representable values of type 'int'
   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/qtrob/dev/src/qt-dev_01.10-base_svg/qtbase/src/gui/kernel/../../corelib/global/qglobal.h:790:14 in
   

Google's oss-fuzz found this as issue 43998. To be precise, that report is about the overflow in qrect.h:183:46. They will publish the report on April 25th.