Undefined behaviour in `vsnprintf_wrapper`

[EliteTK]

Currently vsnprintf_wrapper invokes va_copy but does not invoke va_end before return.

N3220§7.16.1p1

... Each invocation of the va_start and va_copy macros shall be matched by a corresponding invocation of the va_end macro in the same function.

"shall" actually means it's undefined behaviour not to do it, but there is a more explicit statement too:

N3220§7.16.1.3p2

... If there is no corresponding invocation of the va_start or va_copy macro, or if the va_end macro is not invoked before the return, the behavior is undefined.

This is the same wording as in C99 when va_copy was added.