incorrect implementation of mbstowcs and wcstombs

First parameter in wcstombs() and mbstowcs() can be NULL, in this case functions returns the number of characters that would result from conversion.

char rosStr[BUFFER_SIZE] = "Reactos";

cnt = mbstowcs(NULL,rosStr,BUFFER_SIZE);

...

wchar_t rosStr[BUFFER_SIZE] = L"Reactos";

cnt = wcstombs(NULL,rosStr,BUFFER_SIZE);

Example available here:
https://github.com/pechenkin/mailslotBug/blob/master/conversionBug.c