[css-overflow] no-ellipsis and empty string have the same effect

See w3c#12416

Author: frivoal

css-overflow-4/Overview.bs

@@ -746,9 +746,12 @@ Indicating Block-Axis Overflow: the 'block-ellipsis' property</h3>
 			as the <a>block overflow ellipsis</a>
 			at the end of the affected line box.
 			The UA may truncate this string if it is absurdly long.
+
+			When set to the empty string,
+			the behavior is identical to the ''no-ellipsis'' value.
 	</dl>
 
-	When 'block-ellipsis' is not ''no-ellipsis'',
+	When 'block-ellipsis' is neither ''no-ellipsis'' nor the empty string,
 	the <a>block overflow ellipsis</a> string
 	is wrapped in an anonymous inline
 	and placed at the end of the line box