[Error Handling] jwt 관련 에러

### 관련 Issue
jwt 관련 에러

### 어떤 문제인가요?
홈페이지에서 페이지 이동을 계속 진행하다보면
가끔씩 아래와 같은 에러 메세지 출력

### 에러 메시지
```jsx
JsonWebTokenError: jwt malformed
at Object.module.exports [as verify] (/Users/tiahwang/Desktop/Donorticon/server/node_modules/jsonwebtoken/verify.js:63:17)
at get (/Users/tiahwang/Desktop/Donorticon/server/controller/gifticon/gifticon.js:11:24)
at Layer.handle [as handle_request] (/Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/layer.js:95:5)
at next (/Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/route.js:137:13)
at Route.dispatch (/Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/route.js:112:3)
at Layer.handle [as handle_request] (/Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/layer.js:95:5)
at /Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/index.js:281:22
at Function.process_params (/Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/index.js:341:12)
at next (/Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/index.js:275:10)
at Function.handle (/Users/tiahwang/Desktop/Donorticon/server/node_modules/express/lib/router/index.js:174:3)
[nodemon] app crashed - waiting for file changes before starting...
```

### 에러 핸들링 방법

해당 에러코드를 구글에 검색해보니 stackoverflow에서 아래와 같은 게시글 발견
[스택 오버플로우 고고](https://stackoverflow.com/questions/65277469/jsonwebtokenerror-jwt-malformed-creating-an-api-in-expressjs)

일단 저기에 적혀있는데로 코드를 수정해보고
에러가 더이상 생기지 않는지 확인해 볼 필요가 있음

Start by reading the get handler in server/controller/gifticon/gifticon.js and trace how the JWT reaches jsonwebtoken.verify. Reproduce the repeated page navigation that triggers the malformed-token error, then confirm the server no longer crashes and handles the invalid token appropriately.

Written by the indexing model from the issue text.