Segfault on allocator destruction with virtual dtor

[jwt27]

Hi, thanks for this great header, I still use this because of its allocator support. However I just now discovered that it chokes when given an allocator that has a base with virtual destructor.

The following code consistently segfaults upon calling the allocator dtor in templated_call_move_and_destroy():

#include <function.h>

struct A { virtual ~A() { } };

template <typename T = std::byte>
struct Alloc : A
{
    T* allocate(std::size_t) { return nullptr; }
    void deallocate(T*) { }
};

int main()
{
    func::function<int()> f { std::allocator_arg, Alloc<> { }, [] { return 0; } };
    return f();
}