Regularized version gives relative codelength savings as nan if network has no links

[magnusneuman]

Regularized Infomap gives relative codelength savings as nan if network has no links, and the number of modules is equal to the number of nodes. It should be equal to one due to the prior.

[antoneri]

Agent triage:

• Risk: high
• Likely Surface: core
• Verification: make
• Status: runnable