Fix misaligned index in front2back draw loop

[inert-aesthetic]

Fixes #1371

[yuxiaomao]

Change var i = children.length - 1; seems an easier fix; otherwise the else path i = top - 1 needs to be adjusted too ?

[inert-aesthetic]

Change var i = children.length - 1; seems an easier fix; otherwise the else path i = top - 1 needs to be adjusted too ?

You are right, I have changed it to that. Thank you!