Don't allow an empty Subject when creating a Certificate

Misconfiguration (e.g. an empty policy section in the config file) can
lead to an empty Subject. Since certificates should have unique Subjects
this should not be allowed.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5114)

apps/ca.c

@@ -1403,6 +1403,10 @@ static int do_body(X509 **xret, EVP_PKEY *pkey, X509 *x509,
         BIO_printf(bio_err, "The Subject's Distinguished Name is as follows\n");
 
     name = X509_REQ_get_subject_name(req);
+    if (X509_NAME_entry_count(name) == 0) {
+        BIO_printf(bio_err, "Error: The supplied Subject is empty\n");
+        goto end;
+    }
     for (i = 0; i < X509_NAME_entry_count(name); i++) {
         ne = X509_NAME_get_entry(name, i);
         str = X509_NAME_ENTRY_get_data(ne);
@@ -1565,6 +1569,12 @@ static int do_body(X509 **xret, EVP_PKEY *pkey, X509 *x509,
             goto end;
     }
 
+    if (X509_NAME_entry_count(subject) == 0) {
+        BIO_printf(bio_err,
+                   "Error: After applying policy the Subject is empty\n");
+        goto end;
+    }
+
     if (verbose)
         BIO_printf(bio_err,
                    "The subject name appears to be ok, checking data base for clashes\n");