Negative index compilation error tweak

[bbrown683]

This was causing some funky compilation errors for MSVC 14, so i just wrapped them into some macro definitions rather than an array since it appears this was mainly for testing and I did not see them being referenced anywhere else.

[vurtun]

These typedefs are compiled asserts to make sure that user who do not define NK_INCLUDE_FIXED_TYPES are forced to use correct types with correct size. The reasons why you got the compilation error is probably because you either a.) did not define NK_INCLUDE_FIXED_TYPES or b.) did not set the correct types with correct size. If it is none of these two and the problem persists feel free to report back and I will look further into it.

[bbrown683]

Thanks for some clarification on that. The define appears to have solved all the errors and warnings that MSVC reported.