Added Warning when Incorrect dates are inputed

[bpwrs]

An issue occurs when the starting time is later than the ending time but the returned messages are misleading and can make it difficult to spot the typo

Example

Input

time_range_string=["2019-05-20/00:00","2018-09-21/00:01"]
fpi(trange=time_range_string,probe=['1'],data_rate='fast', 
    datatype=['des-moms','dis-moms'],time_clip=True,center_measurement=True)

Output

03-Sep-25 12:13:14: Searching for local files...
03-Sep-25 12:13:14: Searching for local files...
03-Sep-25 12:13:14: No matching CDF versions found.

The exact point where the code breaks is line 67 in mms_get_local_files.py
days = rrule(DAILY, dtstart=parse(parse(trange[0]).strftime('%Y-%m-%d')), until=parse(trange[1])-timedelta(seconds=1))
where rrule returns an empty list. Suggest a check somewhere around here in the code to verify the start time is before the end time.