Fix: 'openssl ca' command crashes when used with 'rand_serial' option

Commit ffb46830e2df introduced the 'rand_serial' option. When it is used,
the 'serialfile' does not get initialized, i.e. it remains a NULL pointer.
This causes a crash when the NULL pointer is passed to the rotate_serial()
call.

This commit fixes the crash and unifies the pointer checking before
calling the rotate_serial() and save_serial() commands.

Fixes #7412

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7417)

apps/ca.c

@@ -976,7 +976,7 @@ end_of_options:
             BIO_printf(bio_err, "Write out database with %d new entries\n",
                        sk_X509_num(cert_sk));
 
-            if (!rand_ser
+            if (serialfile != NULL
                     && !save_serial(serialfile, "new", serial, NULL))
                 goto end;
 
@@ -1044,7 +1044,8 @@ end_of_options:
 
         if (sk_X509_num(cert_sk)) {
             /* Rename the database and the serial file */
-            if (!rotate_serial(serialfile, "new", "old"))
+            if (serialfile != NULL
+                    && !rotate_serial(serialfile, "new", "old"))
                 goto end;
 
             if (!rotate_index(dbfile, "new", "old"))
@@ -1177,10 +1178,9 @@ end_of_options:
         }
 
         /* we have a CRL number that need updating */
-        if (crlnumberfile != NULL)
-            if (!rand_ser
-                    && !save_serial(crlnumberfile, "new", crlnumber, NULL))
-                goto end;
+        if (crlnumberfile != NULL
+                && !save_serial(crlnumberfile, "new", crlnumber, NULL))
+            goto end;
 
         BN_free(crlnumber);
         crlnumber = NULL;
@@ -1195,9 +1195,10 @@ end_of_options:
 
         PEM_write_bio_X509_CRL(Sout, crl);
 
-        if (crlnumberfile != NULL) /* Rename the crlnumber file */
-            if (!rotate_serial(crlnumberfile, "new", "old"))
-                goto end;
+        /* Rename the crlnumber file */
+        if (crlnumberfile != NULL
+                && !rotate_serial(crlnumberfile, "new", "old"))
+            goto end;
 
     }
     /*****************************************************************/