Clessig/develop/fix loss 678 (ecmwf#679)

* Changed logging level for some messages.

* Fixing bug with incorrect counting

Author: clessig

src/weathergen/train/loss_calculator.py

@@ -326,8 +326,8 @@ def compute_loss(
                     loss_fstep = loss_fstep + (loss_fct_weight * loss_lfct * strm_loss_weight)
                     ctr_fsteps += 1 if loss_lfct > 0.0 else 0
 
-                loss = loss + loss_fstep / ctr_fsteps if ctr_fsteps > 0 else loss
-                ctr_streams += 1 if loss_fstep > 0 else 0
+            loss = loss + (loss_fstep / (ctr_fsteps if ctr_fsteps > 0 else 1.0))
+            ctr_streams += 1 if ctr_fsteps > 0 else 0
 
             # normalize by forecast step
             losses_all[strm.name] /= ctr_fsteps if ctr_fsteps > 0 else 1.0