Starting with version 1.893, Email::Address returns undef
if passed non-ASCII email addresses to parse.

Track such email parsing failures in ParseSenderAddressFromHead and
pass them back as an optional third parameter. This allows the
caller to report the error if desired. Failure to parse one message
will generate an error, but the function can still find and return
a valid address from another header. This function is
called from several places and returning the error rather than reporting
avoids multiple warnings from parsing the same emails.

ParseSenderAddressFromHead still reports a failure to find a sender
in any header, since that is an error. That message will be reported
multiple times, one for each call to the function.

Update MailFrom.pm's GetCurrentUser to report the parse failures
as a warning. These parse failures are reported even if a sender
was found in another header. Also update the existing error in
GetCurrentUser to indicate that a parsing failure can also
prevent finding a valid sender.