Fix loading the amp scaler from a checkpoint 🛠️

TTS/trainer.py

@@ -306,7 +306,7 @@ class Trainer:
             model.load_state_dict(checkpoint["model"])
             print(" > Restoring Optimizer...")
             optimizer = _restore_list_objs(checkpoint["optimizer"], optimizer)
-            if "scaler" in checkpoint and self.use_amp_scaler:
+            if "scaler" in checkpoint and self.use_amp_scaler and checkpoint["scaler"]:
                 print(" > Restoring AMP Scaler...")
                 scaler = _restore_list_objs(checkpoint["scaler"], scaler)
         except (KeyError, RuntimeError):