mujoco.FatalError: Offscreen framebuffer is not complete, error 0x8cdd

I'm getting this error while using the EGL rendering backend:

`mujoco.FatalError: Offscreen framebuffer is not complete, error 0x8cdd`

The error is rare (but still fatal for a long job) so not sure if I can provide a script to reproduce. I believe this might be a known issue though? Thanks so much!

The full traceback:

``` File "/acme/environment_loop.py", line 176, in run
result = self.run_episode()
File "/acme/environment_loop.py", line 94, in run_episode
timestep = self._environment.reset()
File "/acme/wrappers/base.py", line 55, in reset
return self._environment.reset()
File "/acme/wrappers/single_precision.py", line 40, in reset
return self._convert_timestep(self._environment.reset())
File "/dm_control/composer/environment.py", line 339, in reset
return self._reset_attempt()
File "/dm_control/composer/environment.py", line 349, in _reset_attempt
self._recompile_physics_and_update_observables()
File "/dm_control/composer/environment.py", line 243, in _recompile_physics_and_update_observables
self._observation_updater.reset(self._physics_proxy, self._random_state)
File "/dm_control/composer/observation/updater.py", line 165, in reset
enabled.observation_callable())
File "/dm_control/composer/observation/observable/mjcf.py", line 266, in get_observation
pixels = physics.render(
File "/dm_control/mujoco/engine.py", line 216, in render
camera = Camera(
File "/dm_control/mujoco/engine.py", line 695, in __init__
if self._physics.contexts.mujoco is not None:
File "/dm_control/mujoco/engine.py", line 526, in contexts
self._make_rendering_contexts()
File "/dm_control/mujoco/engine.py", line 512, in _make_rendering_contexts
mujoco_context = wrapper.MjrContext(self.model, render_context)
File "/dm_control/mujoco/wrapper/core.py", line 606, in __init__
ptr = ctx.call(mujoco.MjrContext, model.ptr, font_scale)
File "/dm_control/_render/executor/render_executor.py", line 138, in call
return func(*args, **kwargs)
mujoco.FatalError: Offscreen framebuffer is not complete, error 0x8cdd
(EnvironmentLoop pid=593400) Exception ignored in:
(EnvironmentLoop pid=593400) Traceback (most recent call last):
(EnvironmentLoop pid=593400) File "/dm_control/mujoco/wrapper/core.py", line 636, in __del__
(EnvironmentLoop pid=593400) self.free()
(EnvironmentLoop pid=593400) File "/dm_control/mujoco/wrapper/core.py", line 624, in free
(EnvironmentLoop pid=593400) ptr = self.ptr
(EnvironmentLoop pid=593400) File "/dm_control/mujoco/wrapper/core.py", line 614, in ptr
(EnvironmentLoop pid=593400) return self._ptr()
(EnvironmentLoop pid=593400) AttributeError: 'MjrContext' object has no attribute '_ptr'```

从 dm_control/mujoco/engine.py 中 _make_rendering_contexts 附近以及 wrapper/core.py 中 MjrContext 附近开始，以报告中的 EGL 后端和 traceback 作为切入点。调查间歇性的 offscreen framebuffer 失败，以及随后出现的缺少 _ptr 清理的错误；完成的标准是得到可复现的诊断，并确认修复有效或记录明确的限制。

由索引模型根据 Issue 内容生成。