Not quite sure why {rBd37d17019c52} forcefully set the Mesh to NULL if
in editmode, but this caused the attribute lookup to fail/crash.
Now only use the attribute if we have the mesh (reducing the scope where
it is used), bmesh editmode case does not rely on it.
Maniphest Tasks: T102318
Differential Revision: https://developer.blender.org/D16406