MDEV-6625 SHOW GRANTS for current_user_name@wrong_host_name

mysql-test/r/grant5.result

+SHOW GRANTS FOR root@invalid_host;
+ERROR 42000: There is no such grant defined for user 'root' on host 'invalid_host'

mysql-test/t/grant5.test

+-- source include/not_embedded.inc
+
+#
+# MDEV-6625 SHOW GRANTS for current_user_name@wrong_host_name
+#
+--error ER_NONEXISTING_GRANT
+SHOW GRANTS FOR root@invalid_host;

sql/sql_parse.cc

@@ -4335,8 +4335,9 @@ case SQLCOM_PREPARE:
     if (!grant_user)
       goto error;
 
-    if (grant_user->user.str &&
-        !strcmp(thd->security_ctx->priv_user, grant_user->user.str))
+    if (grant_user->user.str && grant_user->host.str &&
+        !strcmp(thd->security_ctx->priv_user, grant_user->user.str) &&
+        !strcmp(thd->security_ctx->priv_host, grant_user->host.str))
       grant_user->user= current_user;
 
     if (grant_user->user.str == current_user.str ||