[C] Winapi Call Dynamically and easily

[mcp]

Well, if the code yields UB, that needs to be fixed since it violates the C++ standard. This code violates assumptions made by the compiler when reasoning about/optimizing your program - I shouldn't have to get your program to crash. Above reasoning should already convince you that this code needs to be fixed.
Also, I would move the caching outside of the function, or simply use a mutex - these are much faster than people usually assume, and always safe.