Check return value after loading config file

CLA: trivial
Reviewed-by: NPaul Yang <kaishen.yy@antfin.com>
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/10607)

(cherry picked from commit dd0139f416257ec5632414ed3ad8c61d07ba07ec)

apps/req.c

@@ -435,12 +435,14 @@ int req_main(int argc, char **argv)
 
     if (verbose)
         BIO_printf(bio_err, "Using configuration from %s\n", template);
-    req_conf = app_load_config(template);
+    if ((req_conf = app_load_config(template)) == NULL)
+        goto end;
     if (addext_bio) {
         if (verbose)
             BIO_printf(bio_err,
                        "Using additional configuration from command line\n");
-        addext_conf = app_load_config_bio(addext_bio, NULL);
+        if ((addext_conf = app_load_config_bio(addext_bio, NULL)) == NULL)
+            goto end;
     }
     if (template != default_config_file && !app_load_modules(req_conf))
         goto end;

apps/ts.c

@@ -282,7 +282,8 @@ int ts_main(int argc, char **argv)
         goto end;
     }
 
-    conf = load_config_file(configfile);
+    if ((conf = load_config_file(configfile)) == NULL)
+        goto end;
     if (configfile != default_config_file && !app_load_modules(conf))
         goto end;