[css-overflow-4] Tweak note on line-clamp and webkit-box

Since -webkit-legacy is now a possible value of line-clamp,
the text in the note needed a bit of refinement to clarify that it is
talking about the case where that value is not set.

Author: frivoal

css-overflow-4/Overview.bs

@@ -1176,7 +1176,7 @@ Fragmentation of Overflow: the 'continue' property
 		the [=computed value=] becomes ''inline-block'' and
 		the box establishes a [=BFC=].
 
-	Note: This means that 'line-clamp' will work
+	Note: This means that 'line-clamp' (set without ''line-clamp/-webkit-legacy'') will work
 	if both or neither of ''-webkit-box-orient: vertical''
 	and ''display: -webkit-box'' or ''display: -webkit-inline-box'' are set,
 	but not if ''display: -webkit-box'' or ''display: -webkit-inline-box'' is set