If the BMesh already has a "custom_normal" attribute with the wrong
type, the call to `BM_lnorspace_update` won't be able to add the
attribute with the expected name, and the bevel code ends up using an
invalid offset to access the data.
For the fix, first just guard against that case. But also make sure the
harden normals functionality still works when the input mesh has free
normals. They will no be converted to tangent space normals as
necessary, in bevel and in other BMesh code that requires that
custom normal storage format.
Pull Request: https://projects.blender.org/blender/blender/pulls/143489
f5f9c4f444