st/gui: Do not call prober select in debug scene

src/xrt/state_trackers/gui/gui_scene_debug.c

@@ -226,7 +226,7 @@ on_elem_sink(const char *name, enum u_var_kind kind, void *ptr, void *priv)
 		return;
 	}
 
-	if (p->xp->tracking == NULL) {
+	if (p->xp == NULL || p->xp->tracking == NULL) {
 		return;
 	}
 
@@ -306,8 +306,6 @@ gui_scene_debug(struct gui_program *p)
 
 	gui_scene_push_front(p, &ds->base);
 
-	gui_prober_select(p);
-
 	// Create the sink interceptors.
 	u_var_visit(on_root_enter_sink, on_root_exit_sink, on_elem_sink, p);
 }

src/xrt/state_trackers/gui/gui_scene_main_menu.c

@@ -32,6 +32,12 @@ scene_render(struct gui_scene *scene, struct gui_program *p)
 
 	if (igButton("Debug Test", button_dims)) {
 		gui_scene_delete_me(p, scene);
+
+		// If we have created a prober select devices now.
+		if (p->xp != NULL) {
+			gui_prober_select(p);
+		}
+
 		gui_scene_debug(p);
 	}
 

src/xrt/targets/gui/gui_sdl2_main.c

@@ -34,6 +34,8 @@ main(int argc, char **argv)
 
 	// First scene to start with.
 	if (argc >= 2 && strcmp("debug", argv[1]) == 0) {
+		// We have created a prober select devices now.
+		gui_prober_select(&p.base);
 		gui_scene_debug(&p.base);
 	} else if (argc >= 2 && strcmp("calibrate", argv[1]) == 0) {
 		gui_scene_select_video_calibrate(&p.base);