I verified this change on a corpus of > 200 GB of emails since the mid-90s. With
this change, more addresses parse than before, and anything which parsed before
still parses.

In said corpus, I came across the edge case of comments preceding an
addr-spec (with angle brackets!), e.g. “(John Doe) <john@example.com>”, which
does not satisfy the conditions to be treated as a fallback, as per my reading
of RFC2822.

This change does not parse quoted-strings within comments (a corresponding TODO
is in the code), but I have not seen that in the wild.

Fixes #22670

Change-Id: I526fcf7c6390aa1c219fdec1852f26c514506f76
Reviewed-on: https://go-review.googlesource.com/77474Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>