simplify trainer output

pytorch_lightning/models/trainer.py

@@ -611,10 +611,16 @@ class Trainer(TrainerIO):
 
         try:
             model_specific_tqdm_metrics_dic = output['tqdm_metrics']
-        except TypeError as e:
+        except Exception as e:
             model_specific_tqdm_metrics_dic = {}
 
-        loss = output['loss']
+        # if output dict doesn't have the keyword loss
+        # then assume the output=loss if scalar
+        try:
+            loss = output['loss']
+        except Exception as e:
+            if type(loss) is torch.Tensor:
+                loss = output
 
         self.__add_tqdm_metrics(model_specific_tqdm_metrics_dic)