Make it possible to render an empty level.

main.py

@@ -9,7 +9,7 @@ import pygame.freetype
 
 from gyro import GyroVector, Poincare2Klein
 from constants import I, WHITE, BLACK, IROT, ROT, OFFSET
-from draw import draw
+from draw import draw, DrawnSegment
 from alert import Alert
 from engineevents import EngineEvent, EngineEventProcessingError
 from defaultcontrols import defaultcontrols
@@ -140,7 +140,10 @@ def mainLoop():
         aoEngineEvents = fvControl_ao()
         processevents()
         display.fill(WHITE)
+        if len(level) != 0:
             drawn = draw(level,gPlayer,pi/4,320,iDistScale)
+        else:
+            drawn = [DrawnSegment(0, BLACK)] * 320
         pygame.draw.rect(display,sky,    (0,0,1280,360))
         pygame.draw.rect(display,ground, (0,360,1280,360))
         n = 0