Fix the non-zero area error when adding a slab, ceiling, roof, rail or tiling

Slab, Add Ceiling, Roof, Rail and Tiling all open the 2D sketcher, where you draw a closed shape before applying.

1. Slab, Add Ceiling, Roof, Rail and Tiling all open the 2D sketcher.

   ✓ 已于 2026年10月22日 在产品中核实

2. Discard leaves the sketcher without adding anything.

   ✓ 已于 2026年10月22日 在产品中核实