Add patch from upstream to link to SDL if and only if required
The previous version of CMakeLists.patch unconditionally disabled linking of finderrors to ${SDL2}, which avoided FTBFS when SDL is not available, but caused FTBFS when SDL is available.
Now, finderrors is linked to SDL if and only if it was detected, so that the build will succeed in environments with or without SDL.
Closes: #991343