git-svn bug with blank commits and author file

When trying to import from svn using an author file, git-svn bails out
if it encounters a blank author. The attached patch changes this
behavior and allow using the author file with blanks authors.

I came across this bug while importing from a cvs2svn repo where the
initial revision (1) has a blank author. This doesn't break the behavior
of bailing out when an unknown author is encountered.

Acked-by: Eric Wong <normalperson@yhbt.net>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-svn.perl

@@ -2363,8 +2363,7 @@ sub check_author {
 	my ($author) = @_;
 	if (!defined $author || length $author == 0) {
 		$author = '(no author)';
-	}
-	if (defined $::_authors && ! defined $::users{$author}) {
+	} elsif (defined $::_authors && ! defined $::users{$author}) {
 		die "Author: $author not defined in $::_authors file\n";
 	}
 	$author;