servo: Merge #5887 - layout: Don't panic in border collapse when a row has fewer cells than its previous sibling (from pcwalton:border-collapse-missing-cells); r=mbrubeck

This was seen in Twitter and the Google SERPs (sometimes).

r? @mbrubeck

Source-Repo: https://github.com/servo/servo
Source-Revision: b6fc83cf2b4b426548bb9d10e9493f2b111bd617

servo/components/layout/table.rs

@@ -760,7 +760,9 @@ fn perform_border_collapse_for_row(child_table_row: &mut TableRowFlow,
         let next_block = next_block.push_or_mutate(i, *this_block_border);
         match next_block_borders {
             NextBlockCollapsedBorders::FromNextRow(next_block_borders) => {
-                next_block.combine(&next_block_borders[i]);
+                if next_block_borders.len() > i {
+                    next_block.combine(&next_block_borders[i])
+                }
             }
             NextBlockCollapsedBorders::FromTable(ref next_block_borders) => {
                 next_block.combine(next_block_borders);