The --backend-tls-sni-field is deprecated in favor of sni keyword.
--backend-tls-sni-field still works, and it overrides all sni keyword
in --backend option.  But it will be removed in the future release.

after a call to nghttp2_session_mem_send_internal() which should
set it, however in nghttp2_session_mem_send_internal() it is
possible to return before setting the pointer.

This change initializes the variable to NULL where delcared and
sets the variable in nghttp2_session_mem_send_internal() to
NULL before possibly returning rather than after.

both options are not necessary but are both ideal practice