git-send-email: fix fallback code in extract_valid_address()

In the fallback check, used when Email::Valid is not available, the
extract_valid_address() uses $1 without checking for success of matching
regex. The $1 variable may still hold the result of previous match,
which is the address when email address was in '<>' or be undefined
otherwise.

Now if match fails undefined value is always returned to indicate error.
The same value is used by Email::Valid->address() in that case.

Previously 'foo@bar' address was rejected by Email::Valid and fallback,
but '<foo@bar>' was rejected by Email::Valid, but accepted by fallback.

Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -831,12 +831,12 @@ sub extract_valid_address {
 	$address =~ s/^\s*<(.*)>\s*$/$1/;
 	if ($have_email_valid) {
 		return scalar Email::Valid->address($address);
-	} else {
-		# less robust/correct than the monster regexp in Email::Valid,
-		# but still does a 99% job, and one less dependency
-		$address =~ /($local_part_regexp\@$domain_regexp)/;
-		return $1;
 	}
+
+	# less robust/correct than the monster regexp in Email::Valid,
+	# but still does a 99% job, and one less dependency
+	return $1 if $address =~ /($local_part_regexp\@$domain_regexp)/;
+	return undef;
 }
 
 # Usually don't need to change anything below here.