Fix memory leaks in the Certificate extensions code

After collecting extensions we must free them again.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2284)

ssl/statem/statem_clnt.c

diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index 80ae480..6599d43 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -1425,8 +1425,11 @@
             if (!tls_collect_extensions(s, &extensions, EXT_TLS1_3_CERTIFICATE,
                                         &rawexts, &al)
                     || !tls_parse_all_extensions(s, EXT_TLS1_3_CERTIFICATE,
-                                                 rawexts, x, chainidx, &al))
+                                                 rawexts, x, chainidx, &al)) {
+                OPENSSL_free(rawexts);
                 goto f_err;
+            }
+            OPENSSL_free(rawexts);
         }
 
         if (!sk_X509_push(sk, x)) {