Protect against crash in the `relation_possible` predicate with ambiguous relations. It was still possible to get a KeyError when using relations that are ambiguous at both ends, like (Executable, version_of, Program) & (Version, version_of, Project). Closes #3010148.

sync_schema_props_perms(('State', 'state_of', 'Workflow'), commit=False)
sync_schema_props_perms(('State', 'name', 'String'))