(legacy) unbound renders some illegal output for empty ipv6, closes...

(legacy) unbound renders some illegal output for empty ipv6, closes https://github.com/opnsense/core/issues/738

src/etc/inc/unbound.inc

@@ -162,11 +162,11 @@ EOF;
         $active_interfaces = explode(",", $config['unbound']['active_interface']);
         foreach($active_interfaces as $ubif) {
             $intip = get_interface_ip($ubif);
-            if (!is_null($intip)) {
+            if (!empty($intip)) {
                 $bindints .= "interface: $intip\n";
             }
             $intip = get_interface_ipv6($ubif);
-            if (!is_null($intip)) {
+            if (!empty($intip)) {
                 $bindints .= "interface: $intip\n";
             }
         }
@@ -182,11 +182,11 @@ EOF;
         $outgoing_interfaces = explode(",", $config['unbound']['outgoing_interface']);
         foreach($outgoing_interfaces as $outif) {
             $outip = get_interface_ip($outif);
-            if (!is_null($outip)) {
+            if (!empty($outip)) {
                 $outgoingints .= "outgoing-interface: $outip\n";
             }
             $outip = get_interface_ipv6($outif);
-            if (!is_null($outip)) {
+            if (!empty($outip)) {
                 $outgoingints .= "outgoing-interface: $outip\n";
             }
         }
@@ -687,13 +687,13 @@ function unbound_acls_config() {
     $bindints = "";
     foreach($active_interfaces as $ubif => $ifdesc) {
         $ifip = get_interface_ip($ubif);
-        if (!is_null($ifip)) {
+        if (!empty($ifip)) {
             $subnet_bits = get_interface_subnet($ubif);
             $subnet_ip = gen_subnet($ifip, $subnet_bits);
             $aclcfg .= "access-control: {$subnet_ip}/{$subnet_bits} allow\n";
         }
         $ifip = get_interface_ipv6($ubif);
-        if (!is_null($ifip)) {
+        if (!empty($ifip)) {
             $subnet_bits = get_interface_subnetv6($ubif);
             $subnet_ip = gen_subnetv6($ifip, $subnet_bits);
             $aclcfg .= "access-control: {$subnet_ip}/{$subnet_bits} allow\n";