Moved clear_screen to CVideo and made use of it instead of calling sdl:🪟:fill directly

Should fix nullptr access violations in the tests.

src/display.cpp

@@ -2468,11 +2468,6 @@ const map_labels& display::labels() const
 	return *map_labels_;
 }
 
-void display::clear_screen()
-{
-	screen_.get_window()->fill(0, 0, 0, 255);
-}
-
 const SDL_Rect& display::get_clip_rect()
 {
 	return map_area();

src/display.hpp

@@ -635,10 +635,6 @@ protected:
 	/// map of hexes where only one unit should be drawn, the one identified by the associated id string
 	exclusive_unit_draw_requests_t exclusive_unit_draw_requests_;
 
-
-	/** Clear the screen contents */
-	void clear_screen();
-
 	/**
 	 * Called near the beginning of each draw() call.
 	 * Derived classes can use this to add extra actions before redrawing

src/editor/editor_display.cpp

@@ -59,7 +59,7 @@ editor_display::editor_display(editor_controller& controller, CVideo& video, rep
 	, brush_locations_()
 	, controller_(controller)
 {
-	clear_screen();
+	video.clear_screen();
 }
 
 void editor_display::add_brush_loc(const map_location& hex)

src/game_display.cpp

@@ -83,7 +83,7 @@ game_display::game_display(game_board& board, CVideo& video, std::weak_ptr<wb::m
 		needs_rebuild_(false)
 {
 	replace_overlay_map(&overlay_map_);
-	clear_screen();
+	video.clear_screen();
 }
 
 game_display* game_display::create_dummy_display(CVideo& video)

src/playsingle_controller.cpp

@@ -273,9 +273,7 @@ LEVEL_RESULT playsingle_controller::play_scenario(const config& level)
 		const bool is_victory = get_end_level_data_const().is_victory;
 
 		if(gamestate().gamedata_.phase() <= game_data::PRESTART) {
-			if(sdl::window* window = gui_->video().get_window()) {
-				window->fill(0, 0, 0, 255);
-			}
+			gui_->video().clear_screen();
 		}
 
 		ai_testing::log_game_end();

src/video.cpp

@@ -328,6 +328,15 @@ void CVideo::set_window_icon(surface& icon)
 	window->set_icon(icon);
 }
 
+void CVideo::clear_screen()
+{
+	if(!window) {
+		return;
+	}
+
+	window->fill(0, 0, 0, 255);
+}
+
 sdl::window *CVideo::get_window()
 {
 	return window.get();

src/video.hpp

@@ -155,6 +155,9 @@ public:
 	 */
 	void set_window_icon(surface& icon);
 
+	/** Clear the screen contents */
+	void clear_screen();
+
 	sdl::window *get_window();
 
 	/**