Fix memory leak in tls_parse_stoc_key_share

Found by oss-fuzz

Reviewed-by: Richard Levitte <levitte@openssl.org>
GH: #2102

ssl/statem/extensions_clnt.c

diff --git a/ssl/statem/extensions_clnt.c b/ssl/statem/extensions_clnt.c
index 70d90e7..6d2ed23 100644
--- a/ssl/statem/extensions_clnt.c
+++ b/ssl/statem/extensions_clnt.c
@@ -1027,6 +1027,7 @@
                                         PACKET_remaining(&encoded_pt))) {
         *al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_TLS_PARSE_STOC_KEY_SHARE, SSL_R_BAD_ECPOINT);
+        EVP_PKEY_free(skey);
         return 0;
     }