[css-grid-1] Ensure that 'take from a baseline-aligned item' and 'tak…

…e from first item in any row' conditions apply together, so if there's no items in the first row you'll still pay attention to the baseline-aligned items in the second row. Separately, rearrange the text so that these conditions read more clearly. Part of #3645.

css-grid-1/Overview.bs

@@ -3639,31 +3639,37 @@ Grid Container Baselines</h3>
 
 	<ol>
 		<li>
-			If any of the <a>grid items</a> whose areas intersect the <a>grid container</a>’s first (last) row
-			participate in <a>baseline alignment</a>,
+			If the [=grid container=] does not contain any [=grid items=],
+			the grid container has no first (last) <a>baseline set</a>,
+			and one is <a lt="synthesize baselines">synthesized</a> if needed
+			according to the rules of its <a>alignment context</a>.
+			Exit from this algorithm.
+
+		<li>
+			Otherwise,
+			find the first (last) row of the [=grid container=]
+			containing at least one [=grid item=].
+
+			If any of the [=grid items=] intersecting this row
+			participate in [=baseline alignment=],
 			the grid container's <a>baseline set</a>
 			is <a lt="generate baselines">generated</a> from
 			the shared <a>alignment baseline</a> of those <a>grid items</a>.
 
-		<li>
-			Otherwise, if the grid container has at least one <a>grid item</a>,
+			Otherwise,
 			the grid container's first (last) baseline set
 			is <a lt="generate baselines">generated</a> from
 			the <a>alignment baseline</a> of the first (last) <a>grid item</a>
-			in row-major <a>grid order</a> (according to the <a>writing mode</a> of the <a>grid container</a>).
-			If the item has no <a>alignment baseline</a> in the grid's inline axis,
+			in <a>grid order</a> (according to the <a>writing mode</a> of the <a>grid container</a>).
+			If the [=grid item=] has no <a>alignment baseline</a> in the grid's inline axis,
 			then one is first <a lt="synthesize baselines">synthesized</a>
 			from its border edges.
-
-		<li>
-			Otherwise, the grid container has no first (last) <a>baseline set</a>,
-			and one is <a lt="synthesize baselines">synthesized</a> if needed
-			according to the rules of its <a>alignment context</a>.
 	</ol>
 
 	<dfn export lt="grid order|grid-modified document order">Grid-modified document order (grid order)</dfn>
 	is the order in which <a>grid items</a> are encountered
-	when traversing the grid's <a>grid cells</a>.
+	when traversing the grid's <a>grid cells</a>
+	in row-major order.
 	If two items are encountered at the same time,
 	they are taken in <a>order-modified document order</a>.