Fix (dask) meta handling in spell functions (backport of !167)

climix/index_functions/spell_functions.py

@@ -31,7 +31,8 @@ class SpellLength(ThresholdMixin, ReducerMixin, IndexFunction):
         data = da.moveaxis(data, axis, -1)
         res = da.reduction(data, self.chunk, self.aggregate,
                            keepdims=True, output_size=4,
-                           axis=-1, dtype=int, concatenate=False)
+                           axis=-1, dtype=int, concatenate=False,
+                           meta=np.array((), dtype=int))
         res = da.ma.masked_array(da.ma.getdata(res),
                                  np.broadcast_to(mask[..., np.newaxis],
                                                  res.shape))
@@ -39,7 +40,7 @@ class SpellLength(ThresholdMixin, ReducerMixin, IndexFunction):
 
     def chunk(self, raw_data, axis, keepdims, computing_meta=False):
         if computing_meta:
-            return np.array((0,), ndim=1, dtype=int)
+            return np.array((), dtype=int)
 
         data = self.condition(raw_data, self.threshold.points)
         chunk_res = self.kernels.chunk(data)