Fix T53129: Cycles missing update when changing image auto refresh.

Previously auto refresh worked, but only if it was already enabled before
starting the viewport render.

source/blender/makesrna/intern/rna_image.c

@@ -174,6 +174,11 @@ static void rna_ImageUser_update(Main *UNUSED(bmain), Scene *scene, PointerRNA *
 	ImageUser *iuser = ptr->data;
 
 	BKE_image_user_frame_calc(iuser, scene->r.cfra, 0);
+
+	if(ptr->id.data) {
+		/* Update material or texture for render preview. */
+		DAG_id_tag_update(ptr->id.data, 0);
+	}
 }