openssl: Fix set up of pkcs12 certificate verification chain

sk_X509_pop will decrease the size of the stack which means that the loop would
end after having added only half of the certificates.

Also make sure that the X509 certificate is freed in case
SSL_CTX_add_extra_chain_cert fails.

lib/vtls/openssl.c

@@ -450,7 +450,6 @@ int cert_stuff(struct connectdata *conn,
       PKCS12 *p12;
       EVP_PKEY *pri;
       STACK_OF(X509) *ca = NULL;
-      int i;
 
       f = fopen(cert_file, "rb");
       if(!f) {
@@ -497,8 +496,8 @@ int cert_stuff(struct connectdata *conn,
         goto fail;
       }
       /* Set Certificate Verification chain */
-      if(ca && sk_X509_num(ca)) {
-        for(i = 0; i < sk_X509_num(ca); i++) {
+      if(ca) {
+        while(sk_X509_num(ca)) {
           /*
            * Note that sk_X509_pop() is used below to make sure the cert is
            * removed from the stack properly before getting passed to
@@ -508,6 +507,7 @@ int cert_stuff(struct connectdata *conn,
            */
           X509 *x = sk_X509_pop(ca);
           if(!SSL_CTX_add_extra_chain_cert(ctx, x)) {
+            X509_free(x);
             failf(data, "cannot add certificate to certificate chain");
             goto fail;
           }