Add sanity check when auto-unsubscribing non-existing folders

program/lib/Roundcube/rcube_imap.php

@@ -2932,6 +2932,10 @@ class rcube_imap extends rcube_storage
             // unsubscribe non-existent folders, remove them from the list
             if (!empty($result) && $name == '*') {
                 $existing = $this->list_folders($root, $name);
+
+                // Try to make sure the list of existing folders is not malformed,
+                // we don't want to unsubscribe existing folders on error
+                if (is_array($existing) && (!empty($root) || count($existing) > 1)) {
                     $nonexisting = array_diff($result, $existing);
                     $result      = array_diff($result, $nonexisting);
 
@@ -2940,6 +2944,7 @@ class rcube_imap extends rcube_storage
                     }
                 }
             }
+        }
 
         return $result;
     }