Win32: fix segfault in WriteConsoleW when debugging in gdb

On Windows XP (not Win7), WriteConsoleW and WriteFile seem to raise and
catch SIGSEGV if the lpNumberOfCharsWritten parameter is NULL. This is not
a problem when executed standalone, but gdb stops execution here (unless
disabled via "handle SIGSEGV nostop").

Fix it by passing a dummy variable.

Signed-off-by: Karsten Blees <blees@dcon.de>
Merge pull request #78 from kblees/kb/fix-segfault-in-gdb

Win32: fix segfault in WriteConsoleW when debugging in gdb