[Web] prevent multiple dual-logins

data/web/inc/triggers.inc.php

@@ -121,6 +121,8 @@ if (isset($_POST["login_user"]) && isset($_POST["pass_user"])) {
 
 if (isset($_SESSION['mailcow_cc_role']) && (isset($_SESSION['acl']['login_as']) && $_SESSION['acl']['login_as'] == "1")) {
 	if (isset($_GET["duallogin"])) {
+    $is_dual = (!empty($_SESSION["dual-login"]["username"])) ? true : false;
+    if (!$is_dual) {
       $duallogin = html_entity_decode(rawurldecode($_GET["duallogin"]));
       if (filter_var($duallogin, FILTER_VALIDATE_EMAIL)) {
         if (!empty(mailbox('get', 'mailbox_details', $duallogin))) {
@@ -141,6 +143,7 @@ if (isset($_SESSION['mailcow_cc_role']) && (isset($_SESSION['acl']['login_as'])
         }
       }
     }
+  }
 }
 
 if (isset($_SESSION['mailcow_cc_role'])) {