neaten up stacking logic in mujoco_dset in gail

baselines/gail/dataset/mujoco_dset.py

@@ -50,7 +50,7 @@ class Mujoco_Dset(object):
         # obs, acs: shape (N, L, ) + S where N = # episodes, L = episode length
         # and S is the environment observation/action space.
         # Flatten to (N * L, prod(S))
-        if len(obs.shape[2:]) != 0:
+        if len(obs.shape) > 2:
             self.obs = np.reshape(obs, [-1, np.prod(obs.shape[2:])])
             self.acs = np.reshape(acs, [-1, np.prod(acs.shape[2:])])
         else: