mimalloc 1.6.7 crash on exit

mimalloc-override.dll crashes with "null pointer access" at the very end of the application (built with MSVC 2017 express).
This happens on Windows 7 Professional, 64 bit.
The same app works fine on Windows 10.

Start by reproducing the exit-time crash in mimalloc-override.dll with the reported MSVC 2017 Express build on 64-bit Windows 7 Professional, then compare the same application on Windows 10. Use a debugger to identify the null-pointer access and capture a minimal reproducer; done means the application exits without the crash on the affected environment.

Written by the indexing model from the issue text.