Rendering hangs on some malformed govspeak

[nacnudus]

Rendering the following malformed govspeak string hangs for ages before failing altogether. It would be more helpful to quickly return an error.

govspeak = <<-END_GOVSPEAK               
$LegislativeList                         
* Item                                   
  $EndLegislativeList                    
END_GOVSPEAK                             
Govspeak::Document.new(govspeak).to_html