Crash when RHS connected to pattern element

1. Create a rule with an element in the RHS
2. Load the GenericGraph pattern language, and connect the RHS element to the inner element.
3. Run this rule on an instance graph, and observe that AToMPM crashes.

Reproduce the crash by creating a rule with a right-hand-side element, loading the GenericGraph pattern language, connecting that element to the inner element, and running the rule on an instance graph. Trace the rule execution from this scenario and identify the failing path; done means the rule runs without AToMPM crashing.

Written by the indexing model from the issue text.