Robustness: removes case of mistaken robustness that was hiding a bug, replacing with assert(). Adds FIXME about obscure possibility for bug.
Robustness: removes case of mistaken robustness that was hiding a bug, replacing with assert(). Adds FIXME about obscure possibility for bug.

Alexpux/Coin3D,Alexpux/Coin3D,Alexpux/Coin3D,Alexpux/Coin3D