Segmentation Fault with MuJoCo

I'm looking to benchmark both dm_control and MuJoCo.

This
```
import gym
from dm_control import suite
env = gym.make('HalfCheetah-v3')
```
yields
```
Traceback (most recent call last):
File "wrappers.pxi", line 1139, in mujoco_py.cymj.PyMjModel._extract_mj_names
AssertionError
Exception ignored in: 'mujoco_py.cymj.PyMjModel._set'
Traceback (most recent call last):
File "wrappers.pxi", line 1139, in mujoco_py.cymj.PyMjModel._extract_mj_names
AssertionError
Segmentation fault (core dumped)
```

whereas this exits gracefully:
```
import gym
env = gym.make('HalfCheetah-v3')
from dm_control import suite
env = gym.make('HalfCheetah-v3')
```
I'm using
```
dm-control 1.0.1
mujoco 2.1.3
mujoco-py 2.1.2.14
gym 0.21.0
```

While I'm happy to keep using this solution, it feels like a hack and a fix would be much appreciated!

Start by reproducing the import-order difference using the listed dm-control, MuJoCo, mujoco-py, and gym versions. Inspect the failure reported in wrappers.pxi and mujoco_py.cymj.PyMjModel._extract_mj_names, then verify that importing dm_control before gym.make no longer causes an assertion followed by a segmentation fault.

Written by the indexing model from the issue text.