Issue

Graph Editor will crash if you open the implementation graph (functional) for a node and then select any node in that graph.

Steps to Reproduce

If you start up and open the marble shader implementation graph, and select the output node then it crashes. Tried with head as of time of writing this. This is on Windows and Mac.

Cause

Seems to be this code which now crashes:
https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/source/MaterialXGraphEditor/Graph.cpp#L804
I don't recall this crashing before so could be a regression, or did exist but is now very easy to repro.