Fix build errors with clang-cl version 19 and newer

[emruiz81]

When upgrading visual studio 2022 to the latest update, clang-cl toolchain updates to versio 19 (from version 17). And a compilation error occurs refered to cast conversions on function pointers, something like this:

error : cast from 'FARPROC' (aka 'int (*)() attribute((stdcall))') to 'PFN_DECODEPOINTER' (aka 'void ()(void *) attribute((stdcall))') converts to incompatible function type [-Werror,-Wcast-function-type-mismatch]

This patch addresses this issue with a two step cast conversion that convinces the compiler.

[oliverportcnc]

It would probably be better to use std::memcpy to copy the pointer value as according to the standard function pointers and data pointers don't have to be the same size. Might prevent other warnings popping up in the future.