Fix an exception in the hyperlink remarkup rule for unparseable URIs
Ref T12526. URIs in the form http://x.y/#http://x.y/# can fail to parse. Catch these cases and ignore them, rather than throwing.
- Added failing test cases, made them pass.
Reviewed By: amckinley
Maniphest Tasks: T12526
Differential Revision: https://secure.phabricator.com/D18666