Check return value after loading config file

CLA: trivial

Reviewed-by: Paul Yang <kaishen.yy@antfin.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/10607)
diff --git a/apps/req.c b/apps/req.c
index b084f10..76bbbeb 100644
--- a/apps/req.c
+++ b/apps/req.c
@@ -476,12 +476,14 @@
 
     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;
diff --git a/apps/ts.c b/apps/ts.c
index 196e97b..c651c8e 100644
--- a/apps/ts.c
+++ b/apps/ts.c
@@ -293,7 +293,8 @@
         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;