Failed to load widgetset or bootstrap for template

[ripla]

Steps to reproduce

1. Create an empty template in webapp/frontend directory of Bakery
2. Replace imports with <link rel="import" href="../../../../../webapp/frontend/bower_components/polymer/polymer.html">
3. Wait for ~10s

Actual result

Expected result

Template loaded normally

Notes

External preview shows these failed loads for the template:

• POST http://localhost:56662/flow/5573/src/main/webapp/frontend/with-template.html?v-1514902460865
• GET http://localhost:56662/project/VAADIN/widgetsets/com.vaadin.designer2.VisualDesignerApplicationWidgetset/com.vaadin.designer2.VisualDesignerApplicationWidgetset.nocache.js
• GET http://localhost:56662/project/VAADIN/themes/valo/styles.css

There are also some successful requests for FW8 resources. It seems that the original request to the template, http://localhost:56662/flow/5573/src/main/webapp/frontend/with-template.html, is the originator of the FW8 requests.

If this is an error situation, showing an error message is fine. But not a Framework load error.

[haiwan]

It could also reproducible with some template in Bakery for Flow. See attached screen recording.
Designer: 3.0.0.alpha24
Bakery: latest version as of now, commit 4c65f05e8220c24eac254fd4fcc28cec266cf55b
designer3-widgetset-bug.zip