[fullscreen] Inconsistency of condition between entering fullscreen and exiting fullscreen (#6)

In conditions of "fullscreen element ready check", the spec says:
> element's node document's top layer contains **no elements whose fullscreen flag is set**, or ...

However in the steps of "collect ancestors":
> While docs's last document has a browsing context container whose node document's top layer **consists of a single element and that single element has its fullscreen flag set**, append that node document to docs.

It means, when we have something in the top layer but nothing is fullscreened yet, it is possible to put an element into fullscreen, because there is no element in the top layer with fullscreen flag set, but we cannot exit fullscreen on this document in this case, because when we collect ancestors, the top layer contains more than a single element, although other elements do not have fullscreen flag.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fullscreen/issues/6