Fix -Wzero-as-null-pointer-constant warnings from THROW_XXX_0

There are a few places which use THROW_ARG_0 or THROW_HANDLE_0 in a context where a pointer value is needed, resulting in -Wzero-as-null-pointer-constant warnings when enabled.

These places could use the _NULL suffixed variants of those macros, except no such variants are currently defined. Alternatively, they could use the explicit value variants with a value of nullptr.