uxa: Prevent attempting to call intel_mode_fini() before PreInit runs

In the Ubuntu xserver it is apparently possible for the Screen to be
deleted prior to being fully initialised. Make sure we don't crash in
that situation!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=55346
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/intel_display.c

@@ -1770,6 +1770,9 @@ intel_mode_fini(intel_screen_private *intel)
 {
 	struct intel_mode *mode = intel->modes;
 
+	if (mode == NULL)
+		return;
+
 	while(!list_is_empty(&mode->crtcs)) {
 		xf86CrtcDestroy(list_first_entry(&mode->crtcs,
 						 struct intel_crtc,