Fix memory leak in tls_parse_ctos_psk()

`sess` is not NULL at this point, and is freed on the success path, but
not on the error path. Fix this by going to the `err` label such that
`SSL_SESSION_free(sess)` is called.

CLA: trivial

Reviewed-by: Saša Nedvědický <[email protected]>
Reviewed-by: Tom Cosgrove <[email protected]>
Reviewed-by: Tomas Mraz <[email protected]>
(Merged from openssl#25643)

(cherry picked from commit b2474b2)

ssl/statem/extensions_srvr.c

@@ -1105,7 +1105,7 @@ int tls_parse_ctos_psk(SSL_CONNECTION *s, PACKET *pkt, unsigned int context,
 
             if (sesstmp == NULL) {
                 SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
-                return 0;
+                goto err;
             }
             SSL_SESSION_free(sess);
             sess = sesstmp;