constructTreeFromCompactHTMLToken should call clearExternalCharacters
https://bugs.webkit.org/show_bug.cgi?id=111248

Reviewed by Adam Barth.

I don't know how to write a test for this.  It's possible characters()
is never accessed from HTMLStackItem::token(), but it's better to be
safe than sorry here.

* html/parser/HTMLDocumentParser.cpp:
(WebCore::HTMLDocumentParser::constructTreeFromCompactHTMLToken):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144543 268f45cc-cd09-0410-ab3c-d52691b4dbfc