Add `std::convert::Infallible` implementantion for `ResponseError`

actix-http/src/error.rs

@@ -158,6 +158,14 @@ impl<E: ResponseError> ResponseError for TimeoutError<E> {
     }
 }
 
+/// Return `INTERNAL_SERVER_ERROR` for `std::convert::Infallible`
+impl ResponseError for std::convert::Infallible {
+    fn error_response(&self) -> Response {
+        // `std::convert::Infallible` should never happen
+        unreachable!()
+    }
+}
+
 #[derive(Debug, Display)]
 #[display(fmt = "UnknownError")]
 struct UnitError;