Don't perform layout on connected components containing just one node

[fedarko]

Don't perform layout on connected components containing just one node

[fedarko]

got algorithm mostly figured out by this point; will implement soon

[fedarko]

One small thing -- I guess this will mean that .gv/.xdot export isn't (easily) doable on 1-node components, then?

(We could "fake" this info, I guess, but I don't think that'd be super valuable? I guess we can do it anyway.)

[fedarko]

Remaining TODOs related to this:

• do some more testing to verify the SPQR layout "faking" is entirely ok
• Add .gv export with the "faked" info if -pg is passed -- this actually seems kind of useless, and IMO it'd be a better use of time to just take a few seconds and mention the lack of gv/xdot export for single-node components in the README.

[fedarko]

After doing some testing -- looks ok.