[css-counter-styles] wording tweak

Author: tabatkins

css-counter-styles/Overview.html

@@ -1918,7 +1918,7 @@ <h3 class="heading settled heading" data-level=7.2 id=ethiopic-numeric-counter-s
 
 		<li>
 			For each group with an odd index (as given in the second step),
-			exceptgroups with a value of zero,
+			except groups which originally had a value of zero,
 			append ፻ U+137B.
 
 		<li>

css-counter-styles/Overview.src.html

@@ -1906,7 +1906,7 @@ <h3 id='ethiopic-numeric-counter-style'>
 
 		<li>
 			For each group with an odd index (as given in the second step),
-			exceptgroups with a value of zero,
+			except groups which originally had a value of zero,
 			append ፻ U+137B.
 
 		<li>