fix: wrap scrollToIndex in requestAnimationFrame (#4132)

Author: mxschll

src/select/parts/virtual-list.tsx

@@ -73,15 +73,18 @@ const VirtualListOpen = forwardRef(
               menuEl: menuRefObject?.current,
             });
           } else {
-            scrollToIndex(index);
+            // Fix for AWSUI-61506.  Defer scroll to next frame to ensure
+            // virtual items are measured after re-render.  When called from
+            // parent's useEffect, measurements may not be ready yet.
+            requestAnimationFrame(() => scrollToIndex(index));
           }
         }
         previousHighlightedIndex.current = index;
       },
       [firstOptionSticky, highlightType.moveFocus, scrollToIndex]
     );
 
-    const stickySize = firstOptionSticky ? virtualItems[0].size : 0;
+    const stickySize = firstOptionSticky ? (virtualItems[0]?.size ?? 0) : 0;
     const withScrollbar = !!width && width.inner < width.outer;
 
     const idPrefix = useUniqueId('select-list-');