fix(zero): error on second set of training eps if model didn't train

 - the zero agent requires (batch_size) examples before it will train. the model was trying to save (and getting Adam optimizer weights 0'd)

Author: justindujardin

libraries/mathy_python/mathy/agents/zero/practice_runner.py

@@ -219,8 +219,8 @@ def train_with_examples(self, iteration, train_examples, model_path=None):
         game = self.get_game()
         new_net = self.get_predictor(game)
         trainer = SelfPlayTrainer(self.config, new_net, action_size=new_net.predictions)
-        trainer.train(train_examples, new_net)
-        new_net.save()
+        if trainer.train(train_examples, new_net):
+            new_net.save()
 
 
 class ParallelPracticeRunner(PracticeRunner):