fix: use request.max_content instead of uninitialized local max_content in flow layout

The local max_content was initialized with all-none values, making the
.or() fallback a no-op. Use request.max_content to correctly propagate
the parent cross-size constraint to child layout computation.

Author: TtTRz

float-pigment-layout/src/algo/flow.rs

@@ -463,7 +463,7 @@ impl<T: LayoutTreeNode> Flow<T> for LayoutUnit<T> {
                     max_content.set_cross_size(
                         axis_info.dir,
                         size.cross_size(axis_info.dir)
-                            .or(max_content.cross_size(axis_info.dir)
+                            .or(request.max_content.cross_size(axis_info.dir)
                                 - child_margin.cross_axis_sum(axis_info.dir)),
                     );
                     let max_content = min_max_limit.normalized_size(max_content);
@@ -644,7 +644,7 @@ impl<T: LayoutTreeNode> Flow<T> for LayoutUnit<T> {
                                         axis_info.dir,
                                         css_size
                                             .cross_size(axis_info.dir)
-                                            .or(max_content.cross_size(axis_info.dir)
+                                            .or(request.max_content.cross_size(axis_info.dir)
                                                 - child_margin.cross_axis_sum(axis_info.dir)),
                                     );
                                     let max_content = min_max_limit.normalized_size(max_content);