[css-flexbox-1] Restore main-size clamping to the multiline special case.

Author: tabatkins

css-flexbox-1/Overview.bs

@@ -2955,7 +2955,8 @@ Flex Container Intrinsic Main Sizes</h4>
 	For this purpose,
 	each item's contribution
 	is capped by the item’s [=flex base size=] if the item is not growable,
-	and floored by the item’s [=flex base size=] if the item is not shrinkable.
+	floored by the item’s [=flex base size=] if the item is not shrinkable,
+	and then further clamped by the item's min and max main sizes.
 
 	<details class=note>
 		<summary>Implications of this algorithm when the sum of flex is less than 1</summary>