Change check_vectors task to skip if requested end is after now, instead of requested start

Fix a bug where the check_vectors task would try to run even if the end of the requested time was in the future. This would then ask for a StateVector check with data that didn't yet exist.

Should help address #614 (closed), though I don't think it fixes it completely (since there appear to be events where this failure happens even for non-EW events, which occur in the past).