Fix perl run-time error

git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@8347 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb

Shorewall-perl/Shorewall/IPAddrs.pm

@@ -134,6 +134,8 @@ sub validate_net( $$ ) {
     my ($net, $vlsm, $rest) = split( '/', $_[0], 3 );
     my $allow_name = $_[1];
 
+    $net = '' unless defined $net;
+
     fatal_error "Missing address" if $net eq '';
     fatal_error "An ipset name ($net) is not allowed in this context" if substr( $net, 0, 1 ) eq '+';