allow .nc files with only one time variable

Author: WilliamArmst

rocketpy/environment/environment.py

@@ -1912,7 +1912,10 @@ def process_forecast_reanalysis(
         # Compute info data
         self.atmospheric_model_init_date = get_initial_date_from_time_array(time_array)
         self.atmospheric_model_end_date = get_final_date_from_time_array(time_array)
-        self.atmospheric_model_interval = get_interval_date_from_time_array(time_array)
+        if (self.atmospheric_model_init_date != self.atmospheric_model_end_date):
+            self.atmospheric_model_interval = get_interval_date_from_time_array(time_array)
+        else:
+            self.atmospheric_model_interval = 0
         self.atmospheric_model_init_lat = lat_list[0]
         self.atmospheric_model_end_lat = lat_list[-1]
         self.atmospheric_model_init_lon = lon_list[0]