quic_tls.c: Precede double free on EVP_MD variable

quic_tls.c: Precede double free on EVP_MD variable

When external quic implementation is used, the variable is not used and
double free happens whe the yield_secret_cb fails.

Resolves: #27504

Signed-off-by: Norbert Pocs <norbertp@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27713)

(cherry picked from commit 258d3a695e32828df7dbda6ee9ae67d31e128f62)