rawsList_filterDate() should handle "rawsObject does not contain requested date range"

[jonathancallahan]

We don't want rawsList_filterDate() to stop() just because a single station doesn't have the requested date range.

Instead, a warning can be issued and that element in the list can be assigned an empty raws object -- one with the same meta but with data obtained with:

  # If no data for requested time range, generate a zero-record dataframe
  data <- dplyr::filter(rawsObj$data, wrccID == "Rumplestiltskin")