Fix SeparateActorCritic

ml-agents/mlagents/trainers/torch/networks.py

         actor_mem, critic_mem = None, None
         if self.use_lstm:
             # Use only the back half of memories for critic
-            actor_mem, critic_mem = torch.split(memories, self.memory_size, -1)
+            actor_mem, critic_mem = torch.split(memories, self.memory_size // 2, -1)
         value_outputs, critic_mem_out = self.critic(
             vec_inputs, vis_inputs, memories=critic_mem, sequence_length=sequence_length
         )
     ) -> Tuple[List[DistInstance], Dict[str, torch.Tensor], torch.Tensor]:
         if self.use_lstm:
             # Use only the back half of memories for critic and actor
-            actor_mem, critic_mem = torch.split(memories, self.memory_size, dim=-1)
+            actor_mem, critic_mem = torch.split(memories, self.memory_size // 2, dim=-1)
         else:
             critic_mem = None
             actor_mem = None