Fix notice in group model, a=chris

diff --git a/src/models/GroupModel.php b/src/models/GroupModel.php
index 197595677..a3662ca6f 100644
--- a/src/models/GroupModel.php
+++ b/src/models/GroupModel.php
@@ -1631,6 +1631,8 @@ class GroupModel extends Model implements MediaConstants
                 if ($current_folders) {
                     list($current_folder, $current_thumb_folder) =
                         $current_folders;
+                } else {
+                    continue;
                 }
             } elseif (!$default_folders) {
                 continue;
@@ -2422,4 +2424,4 @@ class GroupModel extends Model implements MediaConstants
         unset($bots[$i]); //last one will be null
         return $bots;
     }
-}
\ No newline at end of file
+}