helix-term: properly handle libc::kill's failure

I misread the manpage for POSIX `kill` -- it returns `-1` in
the failure case, and sets `errno`, which is retrieved via
`std::io::Error::last_os_error()`, has its string representation printed
out, and then exits with the matching status code (or 1 if, for whatever
reason, there is no matching status code).

helix-term/src/application.rs

@@ -458,7 +458,9 @@ impl Application {
                 };
 
                 if res != 0 {
-                    eprintln!("{}", std::io::Error::from_raw_os_error(res));
+                    let err = std::io::Error::last_os_error();
+                    eprintln!("{}", err);
+                    let res = err.raw_os_error().unwrap_or(1);
                     std::process::exit(res);
                 }
             }