Do not try to explode() return parameter when it already is an array

Civi/RemoteToolsRequest.php

@@ -346,7 +346,7 @@ public function wasExecuted()
      */
     public function getOriginalReturnFields()
     {
-        $return = $this->original_request['return'] ?? '';
+        $return = $this->original_request['return'] ?? [];
         if (is_array($return)) {
             return $return;
         }