Don't fail if child isn't present

[gussmith23]

I am currently manually pruning out irrelevant nodes from my serialized egraph. The unwrap I removed was causing errors when encountering removed children.

I can also add a warning in an else branch, if desired.

[saulshanabrook]

I am not sure about supporting visualizations of incomplete/malformed egraphs… I do think it might be better just to panic here instead of silently ignoring an edge. In egglog, we do omit some nodes sometimes to keep the sizes down and we either replace them with a dummy node or remove the edges as well.

Were you removing them for visualization purposes to help debug something? Or was it for performance?

[gussmith23]

Sorry for slow response. Yes -- i was trying to visualize the egraph during debugging, but pruning to just the interesting nodes. Do you have a better suggestion for doing this?