[ASDisplayNode] Fix a crash in insertSubnode #890

Job	Run time
Build and run tests	3m 35s
Build Texture as a dynamic framework	1m 22s
Build Texture as a static library	1m 45s
Verify that Carthage works	9m 58s
Build examples (examples-pt1)	5m 2s
Build examples (examples-pt2)	4m 33s
Build examples (examples-pt3)	4m 10s
Build examples (examples-pt4)	7m 23s
	37m 48s

Provide feedback