nowcast.utils.py code refactoring (#92)

* Refactoring stack_cascades function in nowcast.utils module
* Add empty line at the end of the file

Author: Fangyh09

pysteps/nowcasts/utils.py

@@ -122,11 +122,10 @@ def stack_cascades(R_d, n_levels, donorm=True):
             if donorm:
                 mu_ = R_d[j]["means"][i]
                 sigma_ = R_d[j]["stds"][i]
-            if j == n_inputs - 1:
-                mu[i] = mu_
-                sigma[i] = sigma_
             R__ = (R_d[j]["cascade_levels"][i, :, :] - mu_) / sigma_
             R_.append(R__)
+        mu[i] = R_d[n_inputs - 1]["means"][i]
+        sigma[i] = R_d[n_inputs - 1]["stds"][i]
         R_c.append(np.stack(R_))
 
     return np.stack(R_c), mu, sigma