issue as an input should throw an error, rather than silently failing

[dsweber2]

an example

epidatr::pub_covidcast(
            source = "hhs",
            signals = "confirmed_admissions_covid_1d",
            geo_type = "state",
            time_type = "day",
            geo_values = "*",
            time_values = epirange(from = "20220101", to = "20220401"),
            issue = "*",
            fetch_args = fetch_args_list(return_empty = TRUE, timeout_seconds = 100)
)

epidatr::pub_covidcast(
            source = "hhs",
            signals = "confirmed_admissions_covid_1d",
            geo_type = "state",
            time_type = "day",
            geo_values = "*",
            time_values = epirange(from = "20220101", to = "20220401"),
            issues = "*",
            fetch_args = fetch_args_list(return_empty = TRUE, timeout_seconds = 100)
)

[nmdefries]

This will be fixed by #201