`forecast_hours` is `int` only if reading a ATCF file that has `OFCL` along with `CARQ`

[SorooshMani-NOAA]

See:

StormEvents/stormevents/nhc/track.py

Lines 1041 to 1047 in ee51dd1

	def unfiltered_data(self, dataframe: DataFrame):
	# fill missing values of MRD and MSLP in the OFCL advisory
	if "OFCL" in self.advisories:
	tracks = separate_tracks(dataframe)
	if all(adv in tracks for adv in ["OFCL", "CARQ"]):
	tracks = correct_ofcl_based_on_carq_n_hollandb(tracks)
	dataframe = combine_tracks(tracks)

The separate_tracks call changes the type from object to int64, but if the condition is not satisfied (i.e. OFCL and CARQ are not in the file) then the dataframes with modified forecast_hours type is ignored.