Data and steps to reproduce

https://public.gi.ucsc.edu/~hickey/debug/gfaffix-cycle/

Note that this is a bug with 0.1.5b but not 0.2.0. But the big problem for me as I (rather urgently) try to get HPRC v2 release graphs ready is that I do not have a version of gfaffix that can process all the graphs.

In particular, when I try to make a CHM13-based graph with HG002 held out I get this issue. And when I try to make the same graph with HG002 included, I get the crash from #17.