radix transform: fix misnamed variable

the _ caused the variable to be optimized away, which is not desired

math/radix_transform/src/main.rs

@@ -103,7 +103,7 @@ async fn main() {
     );
 
     // output dst digits
-    let _writer = {
+    let writer = {
         use std::{
             os::unix::io::FromRawFd
         };
@@ -119,5 +119,7 @@ async fn main() {
 
         src_digits.from_json(unsafe { async_std::fs::File::from_raw_fd(0) }).await;
     }
+
+    drop(writer);
 }