Fix Net::POP3 to avoid undefined value warnings

--- perl-5.8.8.orig/lib/Net/POP3.pm	2004-07-04 01:04:46.000000000 +0200
+++ perl-5.8.8/lib/Net/POP3.pm	2004-07-04 01:50:38.000000000 +0200
@@ -54,7 +54,8 @@
  $obj->autoflush(1);
  $obj->debug(exists $arg{Debug} ? $arg{Debug} : undef);
 
- unless ($obj->response() == CMD_OK)
+ my $response = $obj->response();
+ unless ($response && $response == CMD_OK)
   {
    $obj->close();
    return undef;
