[gnome-builder] html-preview: clear action group when unloading

[Christian Hergert <chergert src gnome org>]

commit 2e0c2c9f9722d153d9e6a0f70834bebcb65beef1
Author: Christian Hergert <chergert redhat com>
Date:   Fri Aug 3 17:14:35 2018 -0700

    html-preview: clear action group when unloading

 src/plugins/html-preview/html_preview.py | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/plugins/html-preview/html_preview.py b/src/plugins/html-preview/html_preview.py
index c23d4c18c..641f053ef 100644
--- a/src/plugins/html-preview/html_preview.py
+++ b/src/plugins/html-preview/html_preview.py
@@ -144,6 +144,7 @@ class HtmlWorkbenchAddin(GObject.Object, Ide.WorkbenchAddin):
         self.workbench.insert_action_group('html-preview', group)
 
     def do_unload(self, workbench):
+        workbench.insert_action_group('html-preview', None)
         self.workbench = None
 
     def install_docutils(self):