Fix asset_task: $mac was not defined

Author: vink78

htdocs/management/asset_tasks.html

@@ -164,6 +164,9 @@
 
 		    # MAC
 		    if ( $d{physaddr} ){
+			my $mac = PhysAddr->validate($d{physaddr});
+			Netdot->throw_user("Invalid MAC: $d{physaddr}")
+			    unless $mac;
 			if ( PhysAddr->search(address=>$mac)) {
 			    $dups{macs}{$mac} = 1;
 			    next;