Fix sale not getting client from delivery

Since the change to person fields, the client on model was not being updated.
The client needs to be properly set so the POS checkout can use it as the
sale's client.

Change-Id: I35cba10f2d4fa11dd8fc73aad1212bd7e1e25e5d
Release 1.8rc6

Change-Id: Iabbbebb7297b4edc08980df2b99dd9ff081001ef