Empty webform displays weight and not required for Add compontent row.

When there are no components, the core tabedrag.js looks to the faux "add component" row in the component table to find the weight column. This row has a colspan to combine the name and form_key columns. tabledrag.js is smart enough to cope with colspans when finding the weight column (although oddly it is smart enough when hiding them). The solution is to not use a colspan and supply an empty form_key only when there are no components.