Attempt to re-open CONIN$ if stdin has been redirected on Windows
This should hopefully fix the problem with --passwd-on-stdin, described
in https://github.com/openconnect/openconnect-gui/issues/101
It doesn't actually work for me in wine, as I get 'Access Denied' when
trying to use ReadConsoleW() on the resulting handle. But wine is strange,
and this at least shouldn't make things any *worse*.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>