Address infinite loop in TreeWalker's nextNode()

See #787 (comment) onward for analysis and test references.

Fixes #787.

Author: annevk

dom.bs

@@ -9519,7 +9519,8 @@ steps:
 
      <li><p>Set <var>sibling</var> to <var>temporary</var>'s <a for=tree>next sibling</a>.
 
-     <li><p>If <var>sibling</var> is non-null, then <a for=iteration>break</a>.
+     <li><p>If <var>sibling</var> is non-null, then set <var>node</var> to <var>sibling</var> and
+     <a for=iteration>break</a>.
 
      <li><p>Set <var>temporary</var> to <var>temporary</var>'s <a for=tree>parent</a>.
     </ol>
@@ -10234,6 +10235,7 @@ Ondřej Žára,
 Peter Sharpe,
 Philip Jägenstedt,
 Philippe Le Hégaret,
+Piers Wombwell,
 Pierre-Marie Dartus,
 prosody—Gab<!-- riel --> Vereable<!-- Gaston --> <!-- Croft -->Context(,
 Ra'Shaun Stovall (Snuggs),