[css-grid] Catch the case where an auto-sized track contains no children; growth limit should be zero.

--HG--
extra : rebase_source : 699edd44b97b4611d5aed050c0e5f239f4970521

Author: tabatkins

css-grid/Overview.bs

@@ -2823,6 +2823,11 @@ Resolve Content-Based Track Sizing Functions</h3>
 			</ol>
 
 			Repeat incrementally for items with greater spans until all items have been considered.
+
+		<li>
+			If any track still has an infinite <a>growth limit</a>
+			(because, for example, it had no items placed in it),
+			set its <a>growth limit</a> to its <a>base size</a>.
 	</ol>
 
 	<p id='extra-space'>

css-grid/Overview.html

@@ -2834,6 +2834,11 @@ <h3 class="heading settled" data-level=10.4 id=algo-content><span class=secno>10
 			</ol>
 
 <p>Repeat incrementally for items with greater spans until all items have been considered.</p>
+
+		<li>
+			If any track still has an infinite <a data-link-type=dfn href=#growth-limit title="growth limit">growth limit</a>
+			(because, for example, it had no items placed in it),
+			set its <a data-link-type=dfn href=#growth-limit title="growth limit">growth limit</a> to its <a data-link-type=dfn href=#base-size title="base size">base size</a>.
 	</ol>
 
 	<p id=extra-space>