function is the wide-character equivalent of the
It searches for the first occurrence of the wide-character string
needle (without its terminating L'\0' character) as a substring in
the wide-character string haystack.
function returns a pointer to the first occurrence of
needle in haystack.
It returns NULL if needle does not occur
as a substring in haystack.
Note the special case:
If needle is the empty wide-character string,
the return value is always haystack itself.