fix missing default

mlair/data_handler/data_handler_wrf_chem.py

@@ -52,6 +52,8 @@ class WrfChemDataHandler(AbstractDataHandler):
 
         if rechunk_values is None:
             self.rechunk_values = {self.time_dim_name: 1}
+        else:
+            self.rechunk_values = rechunk_values
 
         # internal
         self._X = None