xcb: Fix depth iterator methods
xcb: Fix depth iterator methods

https://bugzilla.gnome.org/show_bug.cgi?id=730089

spidermonkdust/vala,spidermonkdust/vala,GNOME/vala,frida/vala,flobrosch/vala-fixes,flobrosch/vala-fixes,rvu95/vala,rvu95/vala,GNOME/vala,frida/vala,spidermonkdust/vala,rvu95/vala,flobrosch/vala-fixes,frida/vala,GNOME/vala,GNOME/vala,frida/vala,frida/vala