-fix bug in animation editor

-fix crash bug in physics motion, closes #1993

2d/motion/engine.cfg

@@ -2,3 +2,10 @@
 
 name="Motion Test"
 main_scene="res://motion.scn"
+
+[display]
+
+width=800
+height=600
+stretch_mode="2d"
+stretch_aspect="keep"