windowscodecs: Implement MetadataHandler_GetValue.

[Dmitry Timoshkov]

Vincent Povirk <madewokherd at gmail.com> wrote:

> > +    case VT_I8:
> > +    case VT_UI8:
> > +    case VT_R8:
> > +        return v1->u.uhVal.QuadPart - v2->u.uhVal.QuadPart;
> 
> Won't this only compare the low part on x86?

In reality the only possible variant type supposed to be seen by this
helper is VT_UI2, everything else is just for the sake of completeness.

-- 
Dmitry.