(legacy) openvpn don't write empty xml tags to avoid issues with backend

src/www/vpn_openvpn_client.php

@@ -264,7 +264,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'GET') {
 
 					foreach (explode(",",$copy_fields) as $fieldname) {
 						$fieldname = trim($fieldname);
-						if(isset($pconfig[$fieldname])) {
+						if(!empty($pconfig[$fieldname])) {
 							$client[$fieldname] = $pconfig[$fieldname];
 						}
 					}

src/www/vpn_openvpn_csc.php

@@ -167,7 +167,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'GET') {
 						// 1 on 1 copy of config attributes
 						foreach (explode(",",$all_form_fields) as $fieldname) {
 								$fieldname = trim($fieldname);
-								if(isset($pconfig[$fieldname])) {
+								if(!empty($pconfig[$fieldname])) {
 										$csc[$fieldname] = $pconfig[$fieldname];
 								}
 						}

src/www/vpn_openvpn_server.php

@@ -329,7 +329,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'GET') {
 
 						foreach (explode(",",$copy_fields) as $fieldname) {
 							$fieldname = trim($fieldname);
-							if(isset($pconfig[$fieldname])) {
+							if(!empty($pconfig[$fieldname])) {
 								$server[$fieldname] = $pconfig[$fieldname];
 							}
 						}