xlib: Don't crash just because the display doesn't expose RANDR
xlib: Don't crash just because the display doesn't expose RANDR

If this happens, XRRGetScreenResources will return NULL, so just treat
that like nothing happened.

https://bugzilla.gnome.org/show_bug.cgi?id=699431

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit 57a79912ac70080a2f9cbe65181a25b00bf1192a)

Distrotech/cogl,Distrotech/cogl,Distrotech/cogl,Distrotech/cogl