Workaround for typeid access violation

[Etienne via Digitalmars-d]

There is a bug regarding unordered object collection in the GC. 
My finalizer accesses another GC-allocated object and the 
application *sometimes* crashes here:

void _d_invariant(Object o)
{   ClassInfo c;

     //printf("__d_invariant(%p)\n", o);

     // BUG: needs to be filename/line of caller, not library 
routine
     assert(o !is null); // just do null check, not invariant check

     c = typeid(o);

         ^--------- this is the crash location

The culprit seems to be these operations:

00007ff6`881f324b 488b4510        mov     rax,qword ptr [rbp+10h]
00007ff6`881f324f 488b10          mov     rdx,qword ptr [rax]
00007ff6`881f3252 488b1a          mov     rbx,qword ptr [rdx] 
ds:00000000`00000000=????????????????

The vtable lookup wants to dereference a null entry. Not sure how 
I can fix this, but in the meantime I think typeid could actually 
add a small check on RDX and return null if that's what it is. 
Any input?