Anim Blend Tree 1D weights issue

[LeXXik]

Followup on #6211

Given the path

Level1.Level2.Dance

During the weights calculation loop in Anim Blend Tree 1D, the leaf node (Dance) would take the full weight (1), which would make its parent (Level2) have a zero weight.

On screenshot:
c1 = Dance
c2 = Level2

This sets the parent weight to zero, which breaks the animation.

If the weight is hardcoded to always return 1, then the animation is played correctly:

Repro:
https://playcanvas.com/project/1205544/overview/blend-tree-forked