Crashes with deleting memory allocated in dlls

Nobody has claimed this yet.

Overall, we have been quite happy with mimalloc except on windows with applications that use qt. There we get random crashes. The most consistent pattern is in debug builds when hitting the destructor of a std::string that was created within a Qt dll (eg the QString::toStdString). Such crashes can have various cases such as mismatched runtimes, but I think we don't have that. And disabling mimalloc makes it go away.

We both link in the override dll and include `mimalloc-new-delete.h` as described in https://microsoft.github.io/mimalloc/overrides.html.

It is not clear to me how that would work in general (how it would intercept new/delete calls in the Qt dll), but my knowledge of the inner workings of dlls is very minimal.

Version 1.6.3 and 1.6.1. Building with make. Visual studio 2017 (various revisions including the most recent).

The report points to Qt DLLs, mimalloc-new-delete.h, the override documentation, and the std::string destructor path from QString::toStdString. Start by reproducing the debug-build crash with Visual Studio 2017 and compare it with mimalloc disabled, focusing on allocation boundaries between the application and DLLs. Done means a minimal reproduction and a confirmed cause or fix for the crash.

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