Hotfix for gdas_arch div/0 (NOAA-EMC#3169)

This fixes a div/0 error when `ARCH_EXPDIR_FREQ=0`.

Resolves NOAA-EMC#3168

ush/python/pygfs/task/archive.py

@@ -487,7 +487,7 @@ def _archive_expdir(self, arch_dict: Dict[str, Any]) -> bool:
         if current_cycle in [first_full, edate]:
             # Always save the first and last
             return True
-        elif (current_cycle - first_full).total_seconds() % freq == 0:
+        elif freq != 0 and (current_cycle - first_full).total_seconds() % freq == 0:
             # Otherwise, the frequency is in hours
             return True
         else: