Fix T75394: Archipack update normals before beveling

The Archipack floor operator bpy.ops.archipack.floor() created a bmesh with
with normals that were zero in all components. This triggered an assert
when calling bmesh.ops.bevel(). Updating the normals prior to the call to
bmesh.ops.bevel() avoids this issue.

Reviewed By: stephen_leger

Differential Revision: https://developer.blender.org/D7364

archipack/archipack_floor.py

@@ -318,6 +318,8 @@ class FloorGenerator(CutAblePolygon, CutAbleGenerator):
             for v in verts:
                 v.co.z = bottom
 
+            bm.normal_update()
+
             # bevel
             if d.bevel:
                 for v in bm.verts: