Fix crash when we don't have a plane to display

ui/ozone/platform/dri/crtc_controller.cc

Index: ui/ozone/platform/dri/crtc_controller.cc
diff --git a/ui/ozone/platform/dri/crtc_controller.cc b/ui/ozone/platform/dri/crtc_controller.cc
index 44c88d68a1d99911bc1b954817442e41695127eb..a94ac18c2b0db65ce754a2390ce5aae2fea9377b 100644
--- a/ui/ozone/platform/dri/crtc_controller.cc
+++ b/ui/ozone/platform/dri/crtc_controller.cc
@@ -63,13 +63,17 @@ bool CrtcController::SchedulePageFlip(HardwareDisplayPlaneList* plane_list,
                                       const OverlayPlaneList& overlays) {
   DCHECK(!page_flip_pending_);
   DCHECK(!is_disabled_);
-  const OverlayPlane& primary = OverlayPlane::GetPrimaryPlane(overlays);
-  DCHECK(primary.buffer.get());
+  const OverlayPlane* primary = OverlayPlane::GetPrimaryPlane(overlays);
+  if (!primary) {
+    LOG(ERROR) << "No primary plane to display on crtc " << crtc_;
+    return true;
+  }
+  DCHECK(primary->buffer.get());
 
-  if (primary.buffer->GetSize() != gfx::Size(mode_.hdisplay, mode_.vdisplay)) {
+  if (primary->buffer->GetSize() != gfx::Size(mode_.hdisplay, mode_.vdisplay)) {
     LOG(WARNING) << "Trying to pageflip a buffer with the wrong size. Expected "
                  << mode_.hdisplay << "x" << mode_.vdisplay << " got "
-                 << primary.buffer->GetSize().ToString() << " for"
+                 << primary->buffer->GetSize().ToString() << " for"
                  << " crtc=" << crtc_ << " connector=" << connector_;
     return true;
   }