Gracefully handle errors applying redlinks

An invalid wikilink like [[Foo&bar]], when it gets through to the
redlink handling, will error out because &bar is not a valid html
entity.  This first repair sets up more gracefull error handling
for failures in redlinking(just show the content without redlinks
applied).  A future fix will also address the html entity in url
problem.

Bug: 58455
Change-Id: Iaa36485325668af4bb7b4556e6dedf9c9d3bf346