Comments not properly stripped

Created by: Ede123

Importing the old unittests (#24) uncovered an issue with stripping comments via --enable-comment-stripping

See unittests/comment-beside-xml-decl.svg

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!-- Oh look a comment -->
<!-- generated by foobar version 20120503 -->
<!-- And another -->
<svg xmlns="http://www.w3.org/2000/svg">
  <!-- This comment is meant to test whether removing a comment before <svg>
       messes up removing comments thereafter -->
  <!-- And this one is meant to test whether iteration works correctly in
       <svg> as well as the document element -->
</svg>

for the failing example