Add handler for RequestMalformedError exceptions

Added a new exception handler for RequestMalformedError to return a 400 status code with error details.

fastapi/exception_handlers.py

@@ -1,5 +1,5 @@
 from fastapi.encoders import jsonable_encoder
-from fastapi.exceptions import RequestValidationError, WebSocketRequestValidationError
+from fastapi.exceptions import RequestMalformedError, RequestValidationError, WebSocketRequestValidationError
 from fastapi.utils import is_body_allowed_for_status_code
 from fastapi.websockets import WebSocket
 from starlette.exceptions import HTTPException
@@ -17,6 +17,15 @@ async def http_exception_handler(request: Request, exc: HTTPException) -> Respon
     )
 
 
+async def request_malformed_exception_handler(
+    request: Request, exc: RequestMalformedError
+) -> JSONResponse:
+    return JSONResponse(
+        status_code=400,
+        content={"detail": jsonable_encoder(exc.errors())},
+    )
+
+
 async def request_validation_exception_handler(
     request: Request, exc: RequestValidationError
 ) -> JSONResponse: