fix empty orbit in atlinopt

[swhite2401]

This PR fixes an issue with atlinopt with twiss_in activated.
When orbit_in was not provided an empty list was returned instead of 6 zeros.
The implementation could be further improved by using twiss_in.ClosedOrbit instead of zeros(6,1), to be discussed
If present the default is twiss_in.ClosedOrbit

[lfarv]

The implementation could be further improved by using twiss_in.ClosedOrbit instead of zeros(6,1)

This is what is done in atlinopt6, I just copied the 4 lines !

[lfarv]

OK

[swhite2401]

Thanks, I checked and this is what is done in pyAT as well so I think we are all good

[lfarv]

@swhite2401 : I think this is not the right place for the fix. atlinopt6 is designed to accept twiss input in any format, so what happens here is a bug in atlinopt6, not atplot. Let me have a look.

[swhite2401]

Well if the rmatrix is missing it will fail... the other option is to provide a function that derives the rmatrix from atlinopt output but do you really want to go in this direction?

[swhite2401]

By the way the same problem is in pyAT

[lfarv]

Of course yes: if R is missing, atlinopt6 (build_sigma) takes alpha and beta from the twiss input. But something must be missing… atlinopt6 has not been tested enough in transfer line mode, thanks @simoneliuzzo. Could you separate the two problems, rollback to commit aa1fd9e and open another PR for atplot?

[lfarv]

By the way the same problem is in pyAT

Another good reason to open a dedicated PR !

[swhite2401]

Ok I roll back the last commit and merge this one.