[FIX] web_editor: prevent traceback on convert single-col align stretch

When converting a row with items that are supposed to be stretch-aligned
we need to set each of its column's height. However this failed when
the row contained less than two columns.

opw-3371134

closes odoo/odoo#127813

X-original-commit: 7df4cc0d9aaccf0dabcc4a7863549b276efaa403
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/backend/convert_inline.js

@@ -980,10 +980,12 @@ function formatTables($editable) {
             row.style.verticalAlign = 'bottom';
         } else if (alignItems === 'stretch') {
             const columns = [...row.querySelectorAll('td.o_converted_col')];
-            const commonAncestor = commonParentGet(columns[0], columns[1]);
-            const biggestHeight = commonAncestor.clientHeight;
-            for (const column of columns) {
-                column.style.height = biggestHeight + 'px';
+            if (columns.length > 1) {
+                const commonAncestor = commonParentGet(columns[0], columns[1]);
+                const biggestHeight = commonAncestor.clientHeight;
+                for (const column of columns) {
+                    column.style.height = biggestHeight + 'px';
+                }
             }
         }
     }