Radient: GLTF Loader does not validate node graph sufficiently

[TheMostDiligent]

RadientGLTFConverter.cpp calls the recursive CreateNode() implementation. It has no cycle check and no depth limit. A malformed cyclic imported graph can therefore recurse indefinitely. An extremely deep, otherwise valid graph can overflow the thread stack.

Recommended fix

Perform graph validation before scheduling any mesh work:

enum class VisitState : Uint8
{
    Unvisited,
    Visiting,
    Complete
};

For every child edge:

• validate the child index,
• increment and validate its parent count,
• reject an edge to a Visiting node,
• allow a Complete node only when it is being referenced by another scene as the same root, not by a second parent.

For scene-less documents, synthesize a scene from nodes whose parent count is zero, not from every node.

Instantiate iteratively using an explicit stack:

struct NodeWork
{
    Uint32          NodeIndex;
    RadientEntityID Parent;
};

That removes recursion depth as an input-controlled resource.