HTTP/3: fixed segfault when using SSL certificates with variables. A QUIC connection doesn't have c->log->data and friends initialized to sensible values. Yet, a request can be created in the certificate callback with such an assumption, which leads to a segmentation fault due to null pointer dereference in ngx_http_free_request(). The fix is to adjust initializing the QUIC part of a connection such that it has all of that in place. Further, this appends logging error context for unsuccessful QUIC handshakes: - cannot load certificate .. while handling frames - SSL_do_handshake() failed .. while sending frames