Fix gspawn-win32-helper.c with newer Microsoft CRTs

Fix gspawn-win32-helper.c with newer Microsoft CRTs

The newer Microsoft CRTs (8.0/2005 and later) impose much stricter
(paranoid) checks on close() being doubly called and the use of
invalid file descriptors.  This makes the calls on the file descriptors
use more caution when using them and only call close() when necessary.

This also adds an (empty) invalid parameter handler* as required by the
newer Microsoft CRTs to prevent the system from aborting the process
when we are checking whether a file descriptor is valid.

[*]: http://msdn.microsoft.com/en-us/library/a9yf33zb.aspx

https://bugzilla.gnome.org/show_bug.cgi?id=693646