throw exception if training, but no model is set to train (because i ran into this wondering what the hell was happening)

vall_e/utils/trainer.py

@@ -126,6 +126,16 @@ def train(
 ):
 	engines = load_engines()
 
+	# validate if there's at least one model to train
+	if training:
+		found = False
+		for name, engine in engines.items():
+			if engine.training:
+				found = True
+				break
+		if not found:
+			raise Exception('Training, but no model loaded set to train...')
+
 	"""
 	if is_local_leader():
 		cfg.dump()