BUG: Workaround for rechunking issue in to_iris (#2046)

Author: AlexHilson

xarray/convert.py

@@ -124,7 +124,10 @@ def to_iris(dataarray):
     # Create the right type of masked array (should be easier after #1769)
     if isinstance(dataarray.data, dask_array_type):
         from dask.array import ma as dask_ma
-        masked_data = dask_ma.masked_invalid(dataarray)
+        # masked_invalid can be applied directly to the dataarray, but
+        # results in a bad chunksize. So instead we use the internal
+        # dask array (#2046)
+        masked_data = dask_ma.masked_invalid(dataarray.data)
     else:
         masked_data = np.ma.masked_invalid(dataarray)