send-email: simplify sendmail aliases comment and blank line recognizer

Replace unnecessarily complex regular expression for recognizing comment
and blank lines in sendmail aliases with idiomatic expressions which
can be easily understood at a glance.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -505,7 +505,7 @@ sub parse_sendmail_alias {
 sub parse_sendmail_aliases {
 	my $fh = shift;
 	while (<$fh>) {
-		if (/^\s*(?:#.*)?$/) { next; }
+		next if /^\s*$/ || /^\s*#/;
 		parse_sendmail_alias($_);
 	}
 }