core: set state in value during gadget_editor.getContent

To be consistent with what the underlying gadget does.

This is needed if we want this snippet to empty the editor:

// user type something in editor
gadget.getContent().then(content => {gadget.changeState({value: ''})})

otherwise the state's value is considered to be still "" and this
changeState does nothing.

product/ERP5/bootstrap/erp5_core/SkinTemplateItem/portal_skins/erp5_core/gadget_editor.js.js

@@ -184,6 +184,10 @@ lockGadgetInQueue, unlockGadgetInQueue, unlockGadgetInFailedQueue*/
           })
           .push(function (editor_gadget) {
             return editor_gadget.getContent.apply(editor_gadget, argument_list);
+          }).push(function (content) {
+            // change state in place, like embedded editor does.
+             gadget.state.value = content[gadget.state.key];
+            return content;
           })
           .push(unlockGadgetInQueue(gadget), unlockGadgetInFailedQueue(gadget));
           /*