nowrap.c - reorder variadic macros

[jonyesno]

... so that va_end comes after vsnprintf's use of ap.

Otherwise an optimising compiler can produce code that segfaults.

I don't know enough about compilers to know why, though this updated va_start -> vsnprintf -> va_end sequence feels appropriate.

Context: I was writing a FreeBSD port for tdu and it defaults to -O2 on non-debug builds.

Thanks for tdu!