Fix Segfault in OwnedEnv::send_and_clear

[scrogson]

This change fixes a segfault we found today. This was the diff that @evnu posted which does indeed fix the segfault.

I built OTP-22.2 with valgrind and ran it before and after, which can be seen here.

[evnu]

This looks good to me. We were missing a call to enif_clear_env before here, which is now done. From the documentation:

The message environment msg_env with all its terms (including msg) is invalidated by a successful call to enif_send. The environment is to either be freed with enif_free_env or cleared for reuse with enif_clear_env. An unsuccessful call will leave msg and msg_env still valid.