Crash in MaterialXCore::Element::setChildIndex() due to off-by-one error in index check

[StefanHabel]

I believe I found an off-by-one crash bug in MaterialXCore::Element::setChildIndex().

Minimal repro via Python bindings:

$ python3 -c 'import MaterialX as mx; d = mx.createDocument(); b = d.addBackdrop(); d.setChildIndex(b.getName(), 1)'
Segmentation fault

Expected behavior:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
LookupError: Invalid child index

Fix:

-    if (index < 0 || index > (int) _childOrder.size())
+    if (index < 0 || index >= (int) _childOrder.size())
     {
         throw Exception("Invalid child index");
     }

Found while working on #342

[jstone-lucasfilm]

This looks like a good catch, thanks @StefanHabel, and feel free to post your fix if you have the bandwidth!

[jstone-lucasfilm]

Thanks for this report, @StefanHabel, as well as for the fix in #1582!

[StefanHabel]

Thanks very much @jstone-lucasfilm ! 🙌