Bugfix to store zeros when current data not available

Sometimes the dimension of the data for the currents in bs.bs_data does not have the same dimension as Thomson. From what I can see, the difference is just the last datapoint. I tried to armor the code against these cases, throwing a warning and updating the description. I will try to understand if this is one of the cases where 'it should fail' later, I prepared the bugfix a while ago and there is still value in not failing immediately. @osauter, if you already have an explanation of why this happens in mind I'll modify it accordingly