fix out of range

com.unity.uiwidgets/Runtime/rendering/paragraph.cs

 
         void _computeChildrenWidthWithMaxIntrinsics(float height) {
             RenderBox child = firstChild;
-            List<PlaceholderDimensions> placeholderDimensions = new List<PlaceholderDimensions>(childCount);
+            List<PlaceholderDimensions> placeholderDimensions = new List<PlaceholderDimensions>(new PlaceholderDimensions[childCount]);
             int childIndex = 0;
             while (child != null) {
                 placeholderDimensions[childIndex] = new PlaceholderDimensions(
 
         void _computeChildrenWidthWithMinIntrinsics(float height) {
             RenderBox child = firstChild;
-            List<PlaceholderDimensions> placeholderDimensions = new List<PlaceholderDimensions>(childCount);
+            List<PlaceholderDimensions> placeholderDimensions = new List<PlaceholderDimensions>(new PlaceholderDimensions[childCount]);
             int childIndex = 0;
             while (child != null) {
                 float intrinsicWidth = child.getMinIntrinsicWidth(height);
 
         void _computeChildrenHeightWithMinIntrinsics(float width) {
             RenderBox child = firstChild;
-            List<PlaceholderDimensions> placeholderDimensions = new List<PlaceholderDimensions>(childCount);
+            List<PlaceholderDimensions> placeholderDimensions = new List<PlaceholderDimensions>(new PlaceholderDimensions[childCount]);
             int childIndex = 0;
             while (child != null) {
                 float intrinsicHeight = child.getMinIntrinsicHeight(width);
                 return;
             }
             RenderBox child = firstChild;
-            _placeholderDimensions = new List<PlaceholderDimensions>(childCount);
+            _placeholderDimensions = new List<PlaceholderDimensions>(new PlaceholderDimensions[childCount]);
             int childIndex = 0;
             while (child != null) {
                 child.layout(