[REG 6.1.3 -> 6.2.0] Loading svg file takes too long

1. Have a build of Qt including qtsvg.
   No sanitizers needed.
2. Build the attached project.

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

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

   time ./report /tmp/report/41331.svg
   

   You will see error messages and it will take too long until the program returns:

   qt.svg: link #a is undefined!
   qt.svg: link #-polytonc is undefined!
   qt.svg: link # is undefined!
   qt.svg: link # is undefined!
   qt.svg: link #directionc is undefined!
   
   real	0m18,880s
   user	0m16,749s
   sys	0m0,072s
   

   While it runs, the program fully occupies a CPU core.

When built on Qt 6.1.3, the program returns immediately:

qt.svg: link #a is undefined!
qt.svg: link #-polytonc is undefined!
qt.svg: link # is undefined!
qt.svg: link # is undefined!
qt.svg: link #directionc is undefined!

real	0m1,139s
user	0m0,061s
sys	0m0,042s

Google's oss-fuzz found this as issue 41331. They will publish the report on February 21st.