QUIC QRL: Fix bug in Handshake packet processing

We automatically dropped Initial keys when receiving a Handshake packet,
but did this regardless of whether the packet was successfully decrypted
and authenticated. Per the RFC, we should only drop Initial keys when
successfully processing a Handshake packet.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19176)
