Fixes #327, 0 min temp causes no temp value available

[Zehen-249]

Fixes #327

def _compute_temperature_values(self, working_input_dict: dict) -> dict:  # compute: derives effective bridge temperature range and rise/fall from IRC 6 thermal inputs
        from osdagbridge.core.utils.codes.irc6_2017 import IRC6_2017

        max_str = working_input_dict.get(KEY_TL_HIGHEST_MAX_TEMP)
        min_str = working_input_dict.get(KEY_TL_LOWEST_MIN_TEMP)
        if not max_str or not min_str or max_str == "—" or min_str == "—":
              print("Value None")
              print(f"Max: {max_str}, Min: {min_str}")
              return {}

        try:
            max_temp = float(max_str)
            min_temp = float(min_str)
        except ValueError:
            return {}

the conditional if not max_str or not min_str or max_str == "—" or min_str == "—": causes the issue.
in python 0 is considered false hence all locations with min temp 0 falls under this conditional.

resolution instead of checking if not max_str chack if max_str is None