Diagram are not well saved when contains an Actor shape

[CamiAndrei]

Steps to reproduce this issue:

• Insert a diagram m that doesn't exist yet in a page
  e.g.: Add in wiki mode: {{diagram reference="Diagram"/}} . "Diagram", doesn't exists.
• Click "Save and View"
• Click "Create diagram"
• Add some content in the diagram with shapes, an "Actor" shape
• Click Save&View
  Save&View it's grayed out and the page is not saved

In the browser's console log the following error message is displayed:

XML Parsing Error: unclosed token
Location: http://.......:8080/xwiki/bin/edit/Sandbox/Diagramm?template=Diagram.DiagramTemplate
Line Number 1, Column 1: Diagram:1:1
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://rt.draw.io/cache?alive. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing).

TypeError: rectangles[(rectangles.length - 1)] is undefined
DiagramEditSheet:604:27

• Click Save. The Save button it's gray-out too.
• Click Preview
• Then Save&View from preview.
• Go to the page where it was inserted
  Only a link to the diagram is displayed. The diagram is not displayed.
• Remove the "Actor" shape
  The diagram is displayed in the page where it was inserted.

Also the diagram are not updated anymore in the pages where they were inserted, if at some point an Actor shape was added in it.

• Add an Actor shape to an existing diagram
• Click Save&View
  Save&View it's grayed out and the page is not saved
• Click Save. The Save button it's gray-out too.
• Click Preview
• Then Save&View from preview.
• Go to the page where it was inserted
  The changes made in the diagram are not updated in the inserted page.

[oanalavinia]

This issue is duplicated to #144 , and as is explained in the comment #144 (comment) the issue is resumed to the problem that if the text is not inserted in a squared shape the diagram cannot be saved.
I have updated the description to specify that it includes Actor shapes as well