Addresses https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-6250

Currently in Alpine Linux (latest, 3.10) in the depends system, one of
the ZeroMQ patches won't apply cleanly because the context around the
patch has changed and Alpine's patch implementation can't handle the
diff.

Some patch implementations can't handle fuzz / too much divergence from
the original code.

This PR just tweaks the context code around the patch so that
less-sophisticated patch implementations (such as on Alpine Linux) can
apply the patch without errors.