CKEdit: Switch to source corrupt page when connection lost or when connection is very slow

Switch to source corrupt page when connection lost or when connection is very slow.

Steps to reproduce (on Firefox):

1) Go to XWiki.
2) Edit page
3) Disconnect from the network (or use some trick to make it very very slow)
4) Switch to source
5) CKEditor enters and infinite loop displaying the message "Failed to perform the conversion"
6) Reestablish connection
7) Your page XWiki syntax is replaced by corrupted HTML