Bug 5383: handleNegotiationResult() level-2 debugs() crash (#1856)

Bug 5383: handleNegotiationResult() level-2 debugs() crash (#1856)

Writing a nil c-string to an std::ostream object results in undefined
behavior. When Security::IoResult::errorDescription is nil, that UB
leads to crashes for some STL implementations. These changes avoid UB
while making higher-level reporting code simpler and safer.

This change alters affected level-1 ERROR test lines a little, including
removing duplicated connection information from clientNegotiateSSL()
message (cache_log_message id=62). That duplication existed because
Squid reports the same Connection info automatically via CodeContext.

New WithExtras() mechanism may be useful for other "low-level debugging
and level-0/1 details for admins ought to differ" cases as well. Today,
the only known debugging context for Security::IoResult is
Security::PeerConnector::suspendNegotiation(), but that is likely to
change as we upgrade TLS callers to library-independent wrappers beyond
the current Security::Accept() and Security::Connect() pair.