Improve error handling of API (#4345)

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* Update attached_notes.ts

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* Refactor

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* Update call.ts

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* ✌️

* Fix

src/server/api/endpoints/username/available.ts

@@ -13,18 +13,16 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	// Get exist
-	const exist = await User
-		.count({
-			host: null,
-			usernameLower: ps.username.toLowerCase()
-		}, {
-			limit: 1
-		});
-
-	// Reply
-	res({
-		available: exist === 0
+	const exist = await User.count({
+		host: null,
+		usernameLower: ps.username.toLowerCase()
+	}, {
+		limit: 1
 	});
-}));
+
+	return {
+		available: exist === 0
+	};
+});