move 'use ParaDNS' into register and eval it

so eventually, plugin tests can run against it, if ParaDNS can be loaded

plugins/async/require_resolvable_fromhost

@@ -1,10 +1,15 @@
 #!perl -w
 
+use strict;
+use warnings;
+
+use Qpsmtpd::Constants;
 use Qpsmtpd::DSN;
-use ParaDNS;
-use Socket;
 use Qpsmtpd::TcpServer;
 
+#use ParaDNS;  # moved into register
+use Socket;
+
 my %invalid  = ();
 my $has_ipv6 = Qpsmtpd::TcpServer::has_ipv6();
 
@@ -19,6 +24,11 @@ sub register {
         }
     }
 
+    eval 'use ParaDNS';
+    if ( $@ ) {
+        warn "could not load ParaDNS, plugin disabled";
+        return DECLINED;
+    };
     $self->register_hook( mail => 'hook_mail_start' );
     $self->register_hook( mail => 'hook_mail_done' );
 }
@@ -26,11 +36,10 @@ sub register {
 sub hook_mail_start {
     my ( $self, $transaction, $sender ) = @_;
     
-    return DECLINED
-      if ( $self->qp->connection->notes('whitelisthost') );
+    return DECLINED if $self->qp->connection->notes('whitelisthost');
+
+    if ( $sender ne '<>' ) {
 
-    if ( $sender ne "<>" ) {
-        
         unless ( $sender->host ) {
             # default of addr_bad_from_system is DENY, we use DENYSOFT here to
             # get the same behaviour as without Qpsmtpd::DSN...
@@ -47,7 +56,7 @@ sub hook_mail_start {
 
         return YIELD;
     }
-    
+
     return DECLINED;
 }