Fix null deref in arc_message() / Add signature margin wrapping / Add arc_get_cv()

[DrRemorse]

Hello,

I fixed a null de-reference in arc_message(), added margin wrapping for signatures, and added arc_get_cv().

Please review my commits. I appreciate your consideration.

Thank you.

[abeverley]

Thanks for this contribution @DrRemorse. Just to note that the PR is against the master branch, whereas it should be against the develop branch instead. It looks like the develop branch already contains a couple of similar fixes (and therefore does not merge cleanly).