upcoming changes to igraph

[schochastics]

Hi,

A revdep check due to upcoming changes to igraph, revealed some issues in your package (see https://github.com/igraph/rigraph/blob/cc3affbc42c9c0b2874f87ea29186212094e1370/revdep/problems.md#pathfindr and igraph/rigraph#1793)

I believe this is due to this PR igraph/rigraph#1828 which forbids NAs in adjacency matrices to avoid unintended side effect.

Feel free to reach out if you need any guidance to fix the issue

[egeulgen]

Hi @schochastics

Thanks for the heads up! I'll try to create a PR to address this shortly.