arlfinder: with fewer_arl_file=true, correctly assign each hour to latest forecast, when possible with minimum number of files

[jdubowy]

e.g. if looking for FW00Z data for 2020-11-16T00:00:00 through 2020-11-17T23:00:00, the 11/16 forecast should be used for the first 24 hours and the 11/17 forecast should be used for the last 24 hours. i.e. For the 12 hour overlap, the later forecast should be used.

This works if fewer_arl_file is false, but not if true.

with -f option:

{
    "files": [
        {
            "last_hour": "2020-11-17T12:00:00",
            "first_hour": "2020-11-16T01:00:00",
            "file": "/data/Met/FW00Z/1km/ARL/2020111600/hysplit-2020111600.t00z.namsf.FW"
        },
        {
            "last_hour": "2020-11-17T23:00:00",
            "first_hour": "2020-11-17T13:00:00",
            "file": "/data/Met/FW00Z/1km/ARL/2020111700/hysplit-2020111700.t00z.namsf.FW"
        }
    ]
}

without -f option:

{
    "files": [
        {
            "file": "/data/Met/FW00Z/1km/ARL/2020111600/hysplit-2020111600.t00z.namsf.FW",
            "first_hour": "2020-11-16T01:00:00",
            "last_hour": "2020-11-17T00:00:00"
        },
        {
            "file": "/data/Met/FW00Z/1km/ARL/2020111700/hysplit-2020111700.t00z.namsf.FW",
            "first_hour": "2020-11-17T01:00:00",
            "last_hour": "2020-11-17T23:00:00"
        }
    ]
}