Some CSS resources are not loaded when an external resource is present on portal_css

[rafaelbco]

When an external CSS resource is registered on the portal_css tool then the resources after this one are not loaded inside the editor frame.

The source of the bug is in the @@tinymce-getstyle view. This view generates a stylesheet that includes the stylesheets in portal_css. However when one of the resources is external the generated stylesheet is malformed. For example:

<!-- @import url(http://localhost:8080/Plone/portal_css/theme/stylesheet1.css); -->
<!-- @import url(http://localhost:8080/Plone/portal_css/theme/stylesheet2.css); -->
https://example.org/external.css
<!-- @import url(http://localhost:8080/Plone/portal_css/theme/stylesheet3.css); -->

In this case stylesheet3.css is not loaded.