more fixes for asText() of HtmlTextArea

git-svn-id: svn://svn.code.sf.net/p/htmlunit/code/trunk@9662 5f5364db-9458-4db8-a492-e30667be6df6
one more test for asText()

git-svn-id: svn://svn.code.sf.net/p/htmlunit/code/trunk@9663 5f5364db-9458-4db8-a492-e30667be6df6