inotify: Further fixes for hard link monitoring support

This gets the G_FILE_MONITOR_WATCH_HARD_LINKS flag to the state where it
doesn’t cause crashes, and essentially acts as a no-op. It will not yet
actually monitor for changes made via hard links.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://bugzilla.gnome.org/show_bug.cgi?id=755721