[👾 Error Handling] Error [ERR_HTTP_HEADERS_SENT]: Cannot remove headers after they are sent to the client

## 어떤 에러인가요?
- 기상청 api를 브라우저에 연결시킬 때 에러가 발생

## 에러 메시지
```jsx
Error [ERR_HTTP_HEADERS_SENT]: Cannot remove headers after they are sent to the client
at new NodeError (node:internal/errors:371:5)
at ServerResponse.removeHeader (node:_http_outgoing:654:11)
at ServerResponse.send (/Users/seonhwa/Desktop/codestates31/ThereWeather/server/node_modules/express/lib/response.js:210:10)
at /Users/seonhwa/Desktop/codestates31/ThereWeather/server/index.js:61:13
at weather (/Users/seonhwa/Desktop/codestates31/ThereWeather/server/controllers/get/weather.js:64:9)
at processTicksAndRejections (node:internal/process/task_queues:96:5)
at async /Users/seonhwa/Desktop/codestates31/ThereWeather/server/index.js:57:5 {
code: 'ERR_HTTP_HEADERS_SENT'
}
```

## 에러 핸들링 방법
```jsx
server/index.js에서 콜백에 쓴 if문에 else문을 처리하지 않아 생겼던 것으로 추측하고 수정함
```

## 에러 핸들링을 위해 참고한 레퍼런스 링크
[예시1](https://cocoon1787.tistory.com/714)