ossl_quic_sstream_get_buffer_avail
size_t ossl_quic_sstream_get_buffer_avail(QUIC_SSTREAM *qss);
size_t avail = ossl_quic_sstream_get_buffer_avail(sstream);
ossl_quic_sstream_get_buffer_avail);
&& ossl_quic_sstream_get_buffer_avail(xso->stream->sstream)
|| !TEST_size_t_eq(ossl_quic_sstream_get_buffer_avail(sstream), 0))