Sync fix from ddns.pm to dhcp.pm for bug 3323752.

git-svn-id: https://svn.code.sf.net/p/xcat/code/xcat-core/trunk@10192 8638fb3e-16cb-4fca-ae20-7b5d299a9bcd

xCAT-server/lib/xcat/plugins/dhcp.pm

@@ -1349,6 +1349,7 @@ sub getzonesfornet {
             die "Not supporting having a mask like $mask on an ipv6 network like $net";
         }
         my $netnum= getipaddr($net,GetNumber=>1);
+        unless ($netnum) { return (); }
         $netnum->brsft(128-$maskbits);
         my $prefix=$netnum->as_hex();
         my $nibbs=$maskbits/4;