• fixed issue #74: don't assume that a further session status change
  (e.g. ended, finalized) exists after the last lap
• improved error handling if there exists no usable lap data for any
  driver (#73, e.g. Imola 2021 FP1)
• fastf1.core.get_session should not quietly return
  fastf1.core.Weekend instead of fastf1.core.Session
  if an invalid event name is given.