Fixed 'Cannot unset string offsets' if AdminBaseController::getPost($post) is not array

classes/adminbasecontroller.php

@@ -610,6 +610,10 @@ class AdminBaseController
      */
     protected function getPost($post)
     {
+        if (!is_array($post)) {
+            return [];
+        }
+
         unset($post['task']);
 
         // Decode JSON encoded fields and merge them to data.