Avoid generating a warning if $fullname{$file} is undefined

Signed-off-by: Nick Woolley <git.wu-lee@noodlefactory.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-cvsexportcommit.perl

@@ -259,7 +259,8 @@ if (@canstatusfiles) {
 	    if $file =~ /^no file /
 		&& $status eq 'Up-to-date';
 
-	$cvsstat{$fullname{$file}} = $status;
+	$cvsstat{$fullname{$file}} = $status
+	    if defined $fullname{$file};
       }
     }
 }