Fixes bug in ActorCriticRecurrent hidden state reset (#50)

* fix bug in rnn hidden state reset

Author: jnskkmhr

rsl_rl/modules/actor_critic_recurrent.py

@@ -95,5 +95,7 @@ def forward(self, input, masks=None, hidden_states=None):
 
     def reset(self, dones=None):
         # When the RNN is an LSTM, self.hidden_states_a is a list with hidden_state and cell_state
+        if self.hidden_states is None:
+            return
         for hidden_state in self.hidden_states:
-            hidden_state[..., dones, :] = 0.0
+            hidden_state[..., dones == 1] = 0.0