Style tweaks following review feedback

Reviewed-by: NRich Salz <rsalz@openssl.org>

ssl/ssl_cert.c

@@ -769,7 +769,7 @@ int ssl_add_cert_chain(SSL *s, WPACKET *pkt, CERT_PKEY *cpk)
     STACK_OF(X509) *chain = NULL;
     X509_STORE *chain_store;
 
-    if (!cpk || !cpk->x509)
+    if (cpk == NULL || cpk->x509 == NULL)
         return 1;
 
     x = cpk->x509;

ssl/statem/statem_clnt.c

@@ -2625,7 +2625,6 @@ int tls_construct_client_verify(SSL *s)
     unsigned char *sig = NULL;
     WPACKET pkt;
 
-
     if (!WPACKET_init(&pkt, s->init_buf)) {
         /* Should not happen */
         SSLerr(SSL_F_TLS_CONSTRUCT_CLIENT_VERIFY, ERR_R_INTERNAL_ERROR);

ssl/t1_lib.c

@@ -3122,7 +3122,8 @@ static int tls12_find_nid(int id, const tls12_lookup *table, size_t tlen)
 int tls12_get_sigandhash(WPACKET *pkt, const EVP_PKEY *pk, const EVP_MD *md)
 {
     int sig_id, md_id;
-    if (!md)
+
+    if (md == NULL)
         return 0;
     md_id = tls12_find_id(EVP_MD_type(md), tls12_md, OSSL_NELEM(tls12_md));
     if (md_id == -1)