HULK console: clear last row when shifting rows up

src/hulk/console.d

@@ -49,6 +49,7 @@ struct console
             fb.copy_rows_up(fb_y(m_height - 1u),
                     (m_height - 1u) * kfont.line_height,
                     kfont.line_height);
+            fb.rect(0u, fb_y(m_height - 1u), fb_x(m_width), kfont.line_height, 0u);
         }
     }