Fix padding calculation in HTMLOptionsCollection's index setter

Correct an off-by-one error in the index setter of HTMLOptionsCollection when the target index is greater than the current length of the collection.

Fixes #11905.

Author: lpas

source

@@ -9805,15 +9805,15 @@ interface <dfn interface>HTMLOptionsCollection</dfn> : <span>HTMLCollection</spa
    <li><p>Let <var>length</var> be the number of nodes <span>represented by the
    collection</span>.</p></li>
 
-   <li><p>Let <var>n</var> be <var>index</var> minus <var>length</var>.</p></li>
+   <li><p>Let <var>delta</var> be <var>index</var> minus <var>length</var>.</p></li>
 
-   <li><p>If <var>n</var> is greater than zero, then <span
-   data-x="concept-node-append">append</span> a <code>DocumentFragment</code> consisting of <span
-   data-x=""><var>n</var>-1</span> new <code>option</code> elements with no attributes and
+   <li><p>If <var>delta</var> is greater than zero, then <span
+   data-x="concept-node-append">append</span> a <code>DocumentFragment</code> consisting of
+   <var>delta</var> new <code>option</code> elements with no attributes and
    no child nodes to the <code>select</code> element on which the <code>HTMLOptionsCollection</code>
    is rooted.</p></li>
 
-   <li><p>If <var>n</var> is greater than or equal to zero, <span
+   <li><p>If <var>delta</var> is greater than or equal to zero, <span
    data-x="concept-node-append">append</span> <var>value</var> to the <code>select</code>
    element. Otherwise, <span data-x="concept-node-replace">replace</span> the <var>index</var>th element in the collection by <var>value</var>.</p></li>
   </ol>
@@ -156518,6 +156518,7 @@ INSERT INTERFACES HERE
   Lobotom Dysmon,
   Logan<!-- on moz irc -->,
   Logan Moore,
+  Lorenz Ackermann,
   Loune,
   Lucas Gadani,
   &#x0141;ukasz Pilorz,