glib/gpoll W32: trust WFMOE() return value

WaitForMultipleObjectsEx() returns the index of the *first* handle that triggered the wakeup, and promises that all handles with lower index are still inactive. Therefore, don't check them, only check the handles with higher index. This removes the need of rearranging the handles (and, now, handle_to_fd) array, it's enough to take a pointer to the next item and use it as a new, shorter array.

https://bugzilla.gnome.org/show_bug.cgi?id=785468