Fix Tuple spaces in rollout.py (#5332)

Make sure that the initial action is also properly flattened.

python/ray/rllib/rollout.py

@@ -132,7 +132,7 @@ def rollout(agent, env_name, num_steps, out=None, no_render=True):
         state_init = {p: m.get_initial_state() for p, m in policy_map.items()}
         use_lstm = {p: len(s) > 0 for p, s in state_init.items()}
         action_init = {
-            p: m.action_space.sample()
+            p: _flatten_action(m.action_space.sample())
             for p, m in policy_map.items()
         }
     else: