Fix so subscribed non-existing/non-accessible shared folder can be unsubscribed

CHANGELOG

@@ -1,6 +1,7 @@
 CHANGELOG Roundcube Webmail
 ===========================
 
+- Fix so subscribed non-existing/non-accessible shared folder can be unsubscribed
 - Rewritten test scripts for PHPUnit
 - Add new DB abstraction layer based on PHP PDO, supporting SQLite3 (#1488332)
 - Removed PEAR::MDB2 package

program/steps/settings/folders.inc

@@ -321,8 +321,8 @@ function rcube_subscription_form($attrib)
                 }
             }
         }
-        // check if the folder is shared, then disable subscription option on it
-        if (!$disabled && $folder['virtual'] && !empty($namespace)) {
+        // check if the folder is shared, then disable subscription option on it (if not subscribed already)
+        if (!$disabled && !$subscribed && $folder['virtual'] && !empty($namespace)) {
             $tmp_ns = array_merge((array)$namespace['other'], (array)$namespace['shared']);
             foreach ($tmp_ns as $item) {
                 if (strpos($folder['id'], $item[0]) === 0) {