Fix intermittent pygame/X11 rendering error

[judithfan]

Seems to arise after ~10 min. of inactivity between rendering calls (display_world.py)

xcb_connection_has_error() returned true
xcb_connection_has_error() returned true
xcb_connection_has_error() returned true
Traceback (most recent call last):
 File “display_world.py”, line 320, in <module>
   RENDER = str2bool(args.RENDER))
 File “display_world.py”, line 209, in random_world_test
   RENDER = RENDER)
 File “display_world.py”, line 86, in display_blocks
   game_display = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT), 0, 32)