[css-syntax-3] Fix the loop *properly*, to not change top-level behav…

…ior of '@foo;;foo{}'.

css-syntax-3/Overview.bs

@@ -2558,7 +2558,8 @@ Consume a qualified rule</h4>
 
  To <dfn>consume a qualified rule</dfn>,
  from a [=token stream=] |input|,
- given an optional bool |nested| (default false):
+ given an optional [=token=] |stop token|
+ and an optional bool |nested| (default false):
 
  Let |rule| be a new [=qualified rule=]
  with its prelude, declarations, and child rules
@@ -2568,10 +2569,9 @@ Consume a qualified rule</h4>
 
  <dl>
  <dt><<EOF-token>>
- <dt><<semicolon-token>>
+ <dt>|stop token| (if passed)
  <dd>
  This is a <a>parse error</a>.
- [=Discard a token=] from |input|.
  Return nothing.
 
  <dt><a href="#tokendef-close-curly">&lt;}-token></a>
@@ -2713,7 +2713,8 @@ Consume a block's contents</h4>
 
  Otherwise, [=restore a mark=] from |input|,
  then [=consume a qualified rule=] from |input|,
- with |nested| set to true.
+ with |nested| set to true,
+ and <<semicolon-token>> as the |stop token|.
  If a [=rule=] was returned,
  append it to |rules|.
  </dl>