RegisterPage: don't display spinning icon after next()
RegisterPage: don't display spinning icon after next()

This is only noticeable if they get to the FinalPage and then press
"back", but it's still worth fixing.

Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui