fix ema params not changing at all if disabled

shadow params should just be the same as the model params
by not updating at all then they just stay as the original init model params (ie random)

src/ml_downscaling_emulator/score_sde_pytorch/models/ema.py

@@ -51,6 +51,9 @@ def update(self, parameters):
         parameters = [p for p in parameters if p.requires_grad]
         for s_param, param in zip(self.shadow_params, parameters):
           s_param.sub_(one_minus_decay * (s_param - param))
+    else:
+      # if disabled then just maintain a copy of the parameters
+      self.shadow_params = [p.clone().detach() for p in parameters if p.requires_grad]
 
   def copy_to(self, parameters):
     """