nanshe/nanshe/registration.py: Only remove global shifts if there is more than one frame.
nanshe/nanshe/registration.py: Only remove global shifts if there is more than one frame.

jakirkham/nanshe,jakirkham/nanshe,nanshe-org/nanshe,DudLab/nanshe,DudLab/nanshe,nanshe-org/nanshe