make update_log() work if zone is not set

Merged Evan Hunt requested to merge update-log-fix into master

update_log() is called to log update errors, but if those errors occur before the zone is set (for example, when returning NOTAUTH) it returns without logging anything.

This doesn't need a CHANGES note; it doesn't modify any existing log messages, it just makes some appear that weren't appearing.

Merge request reports