Unclosed {{html}} results in addition of closing tag even when macro isn't actually evaluated

Repro:

1. Add the following anywhere within a wiki page and save it:

{{code}}{{html}}{{/code}}

2. Edit the wiki page with CKEditor.
3. Observe that

{{/html}}

gets automatically added to the end of the page content.

Since the html macro was not actually evaluated as a macro, XWiki shouldn't be trying to close its tag in this way; it should have simply have been treated in the same way a verbatim block is treated.

An arguably even worse outcome can be obtained by using the following markup:

{{html wiki=true}}{{{{{html}}}}}{{/html}}

In this case, if you save and edit, you will have some messy transformation of the original markup appearing in CKEditor. CKEditor will then "fail to perform conversion" if you switch to Source view.

I ran into these problem cases when trying to create howto guides for the use of the html macro.