fixed switch warning(finally)

src/mandelbrot.c

@@ -479,6 +479,8 @@ main(int argc, char **argv)
                             case SDL_SCANCODE_H:
                                 app.draw_ui = 1 - app.draw_ui;
                                 break;
+                            default:
+                                break;
                         }
                 default:
                     //returns one if recalc needed