[css-properties-values-api] Fix syntax string parsing to not treat whitespace between components the same as pipes.

Fixes w3c#893

Author: emilio

css-properties-values-api/Overview.bs

@@ -596,19 +596,15 @@ Parsing the syntax string {#parsing-syntax}
 			return |descriptor|;
 			otherwise, return failure.
 
-		:   U+007C VERTICAL LINE (|)
+		:   anything else
 		:: If |descriptor|’s [=list/size=] is greater than zero,
-			<a>consume a syntax component</a> from |stream|.
-			If failure was returned,
+			and the <a>current input code point</a> is not U+007C VERTICAL LINE (|),
 			return failure;
-			otherwise,
-			[=list/append=] the returned value to |descriptor|.
 
-			If |descriptor|’s [=list/size=] is zero, return failure.
+		:: If the <a>current input code point</a> is not U+007C VERTICAL LINE (|),
+			<a>Reconsume the current input code point</a> in |stream|.
 
-		:   anything else
-		:: <a>Reconsume the current input code point</a> in |stream|.
-			<a>Consume a syntax component</a> from |stream|.
+		:: <a>Consume a syntax component</a> from |stream|.
 			If failure was returned,
 			return failure;
 			otherwise,