egl: set TSD as NULL after deinit
When eglReleaseThread() is called from application's destructor (API with attribute((destructor))), it crashes due to invalid memory access.
In this case, _egl_TLS is freed in the flow of _eglAtExit() as below but _egl_TLS is not set to NULL.
_eglDestroyThreadInfo
|__ _eglFiniTSD
|__ _eglAtExit
|__ __run_exit_handlers
|__ exit
Later when the eglReleaseThread is called from application's destructor, it ends-up accessing the freed _egl_TLS pointer.
eglReleaseThread -> in libEGL_mesa
|__ eglReleaseThread -> in libEGL(glvnd)
|__ destructor() -> App's destructor
To resolve the invalid access, setting the _egl_TLS pointer as NULL after freeing it.