Minor bug in *wscanf in 2.2.4

[Jason Merrill]

In the following testcase, swscanf should return '0', as the scanset does
not match any of the input characters.  Instead, it returns 1 and sets
buf[0] to 0.  The non-wide *scanf functions do not seem to have this bug.

Seen with Red Hat glibc-2.2.4-19.3 rpm.

---
#include <wchar.h>

int main ()
{
  wchar_t buf[10];
  return swscanf (L"foo", L"%[q]", buf);
}