Fix susyprop

This tries to fix the problem reported in gerbaudo/SusyNtuple/14
@amete can you please confirm that the susypropagator bug is affecting only the simplified model samples?
My [commit from last year](https://github.com/gerbaudo/SusyCommon/commit/dea8d16017d3cc30f2d9284cc48e794e02ab3aed)
says `only for c1c1`, but I cannot find more details in my inbox.