FTI - Fix SceneTreeFTI depth limit behaviour

[lawnjelly]

Fixes off by one bug, and increases the limit slightly.

Forward port of #111443
Fixes crash mentioned in #106244 (comment)

Notes

• My bad, simple off by one bug here, so it writes just off the end of the array. It didn't show up in testing because not only does the scene depth need to reach the limit, but one of the nodes past the limit needs to be moved (rather than via a parent).
• I've also increased the limit just a tad from 32 to 48. There's no particularly bad consequence from overrunning the limit (just slightly less efficiency in the interpolation calculations), but there isn't much cost to increasing this. I did consider 64 but users should really not be using such scene depths anyway as it will be super inefficient.

[Ivorforce]

Makes sense to me.

[Repiteo]

Thanks!