product webservice "time" parameter does not work with open intervals

Time parameter currently only matches products that specify starttime and endtime parameters: https://code.usgs.gov/ghsc/hazdev/earthquake-event-ws/-/blob/master/src/lib/classes/pdl/ProductIndex.class.php#L1859-1863

• allow starttime/endtime to be undefined as an open time interval, essentially:

  (product.starttime IS NULL or product.starttime <= time)
  AND (product.endtime IS NULL or product.endtime >= time)