[OpenGEX] Crash when attempt load bundled test OpenGEX 3D model files

Getting crashes when attempting to load bundled OpenGEX models. Reason appears to be that when iterating in `OpenGEXImporter::resolveReferences()`, this line is failing:
```
node->mMeshes[i] = meshIdx;
```
because `i` greater than or equal to value of `node->mNumMeshes`.

Can easily observe this problem by adding logging around that line in `OpenGEXImporter::resolveReferences()` e.g.
```
if (i < node->mNumMeshes) {
node->mMeshes[i] = meshIdx;
// Log success...
} else {
// Log failure...
}
```

Affected models:

Model
test/models/OpenGEX/animation_example.ogex
test/models/OpenGEX/camera.ogex
test/models/OpenGEX/collada.ogex

Start in OpenGEXImporter::resolveReferences() and reproduce the crash with test/models/OpenGEX/animation_example.ogex, camera.ogex, and collada.ogex. Trace the mesh-reference iteration around node->mMeshes[i] and verify the affected models load without an out-of-bounds access or crash.

Written by the indexing model from the issue text.