Fix base case

Author: jklymak

xmitgcm/mds_store.py

@@ -269,7 +269,6 @@ def open_mdsdataset(data_dir, grid_dir=None,
                 if grid_vars_to_coords:
                     ds = _set_coords(ds)
                 return ds
-
     store = _MDSDataStore(data_dir, grid_dir, iternum, delta_t, read_grid,
                           prefix, ref_date, calendar,
                           geometry, endian,
@@ -656,7 +655,7 @@ def load_from_prefix(self, prefix, chunks=None, iternum=None, extra_metadata=Non
             ddir = self.data_dir
 
         basename = os.path.join(ddir, fname_base)
-        if chunks is None:
+        if chunks is None or isinstance(chunks, dict):
             chunks = "CS" if self.cs else "3D"
 
         try: