Throw 404 error on grid field nested form move-to-parent action,

if no record is found.

src/GridFieldNestedForm.php

@@ -288,7 +288,7 @@ class GridFieldNestedForm extends AbstractGridFieldComponent implements
         $list = $gridField->getList();
         $id = isset($move['id']) ? (int) $move['id'] : null;
         if (!$id) {
-            throw new HTTPResponse_Exception('Missing ID', 400);
+            throw new HTTPResponse_Exception('Missing ID', 404);
         }
         $to = isset($move['parent']) ? (int)$move['parent'] : null;
         // should be possible either on parent or child grid field, or nested grid field from parent

src/GridFieldNestedFormItemRequest.php

@@ -73,7 +73,7 @@ class GridFieldNestedFormItemRequest extends GridFieldDetailForm_ItemRequest
                 }
             }
 
-            if ($this->record->hasExtension(Hierarchy::class)) {
+            if ($this->record->hasExtension(Hierarchy::class) && $relationClass == get_class($this->record)) {
                 $config->addComponent($nestedForm = new GridFieldNestedForm(), GridFieldOrderableRows::class);
                 // use max nesting level from parent component
                 $nestedForm->setMaxNestingLevel($this->component->getMaxNestingLevel());