don't log errors when all is fine
Merge pull request #16145 from phoet/patch-2

don't log errors when all is fine
Fixes the digits counter of AS's NumberToRoundedConverter

Zero has one digit, but Math.log10(0) returns -Infinity. The method
needs to special-case zero.

The patch adds a regression test that is not clearly related to the
underlying issue because digit_count is private and has no coverage.
Gray area.

This bug was uncovered by 60062cf.
Deprecated .deliver / .deliver! to .deliver_now / .deliver_now!
Updated rdoc / guides / release notes related to ActiveJob / ActionMailer