Handle a single carelink basal rate better

@jebeck @jh-bate @kentquirk 

These are the changes to handle a single carelink schedule better.  I tested not only via the unit test, but by pulling the offending data down locally and running it.  It is working.
A number of things would be useful, but I've intentionally kept these messages a little cryptic in order to reduce the chances of leaking information.  Getting the input data, looking up the timestamp and understanding the code combine together to allow for this to be a meaningful message, though not the friendliest.