Do not pass wstring::c_str() to wstringToString function

[dreamer-dead]

It looks that the wstringToString() function can be called with few types of arguments:

• with constructed std::wstring object
• with some WCHAR buf[N] buffer that can be casted to const wchar_t * and this is OK
• with std::wstring("").c_str() pointer and this is the case I am trying to address with this PR

I think that there is no sense to pass a c_str() from a std::wstring object to wstringToString because it will copy the whole string one more time via std::wstring(const wchat_t*) constructor in the end. Also c_str() will always return a zero terminated string and never a nullptr pointer value.

[Smjert]

Good catch!