MINOR: quic: Correctly wait for the completion of handshakes with early data (aws-lc)

MINOR: quic: Correctly wait for the completion of handshakes with early data (aws-lc)

This patch impacts only the haproxy builds against aws-lc TLS stack (USE_OPENSSL_AWSLC).

As mentionned by the boringssl documentation, SSL_do_handshake() completes as soon
as ClientHello is processed and server flight sent (from the TLS stack to the
server endpoint I guess). Into QUIC, the completion has as side effect to discard
the Handshake packet number space. If this handshake completion is not deffered,
the Handshake level CRYPTO data will not be sent to the peer (because of the
assotiated packet number space discarding). According to the documentation,
SSL_in_early_data() may be used to do that. If it returns 1, this means that
the handshake is still in progress but has enough progressed to send half-RTT
data.

This patch is required to make the haproxy builds against aws-lc TLS stack support 0-RTT.