SDK / exoplayer

This is safer because it will prevent any future problems with
creating a new FrameProcessorChain before the previous one has
completed its async release.

From [eglDestroyContext documentation](https://www.khronos.org/registry/EGL/sdk/docs/man/html/eglDestroyContext.xhtml):
"If the EGL rendering context is not current to any thread,
eglDestroyContext destroys it immediately."
The context isn't current to any thread here because GlUtil calls
eglMakeCurrent with EGL_NO_CONTEXT before calling eglDestroyContext.
So everthing should be released once the FrameProcessorChain's
release task terminates.

PiperOrigin-RevId: 442807484