Fix #4484 (#4485)

* Fix #4484

* import order

src/misc/convert-host.ts

@@ -0,0 +1,21 @@
+import config from '../config';
+import { toUnicode, toASCII } from 'punycode';
+
+export function getFullApAccount(username: string, host: string) {
+	return host ? `${username}@${toApHost(host)}` : `${username}@${toApHost(config.host)}`;
+}
+
+export function isSelfHost(host: string) {
+	if (host == null) return true;
+	return toApHost(config.host) === toApHost(host);
+}
+
+export function toDbHost(host: string) {
+	if (host == null) return null;
+	return toUnicode(host.toLowerCase());
+}
+
+export function toApHost(host: string) {
+	if (host == null) return null;
+	return toASCII(host.toLowerCase());
+}