clipmenud: Time out all calls to xsel after 1 second

I'm not entirely sure how this happens, but sometimes xsel gets rather
stuck:

    % systemctl --user status clipmenud
    ● clipmenud.service - Clipmenu daemon
       Loaded: loaded (/usr/lib/systemd/user/clipmenud.service; disabled; vendor preset: enabled)
       Active: active (running) since Wed 2017-03-15 11:14:14 GMT; 1 day 13h ago
     Main PID: 31630 (clipmenud)
       CGroup: /user.slice/user-1000.slice/user@1000.service/clipmenud.service
               ├─ 9052 /bin/bash /usr/bin/clipmenud
               ├─ 9053 xsel --logfile /dev/null -o --primary
               └─31630 /bin/bash /usr/bin/clipmenud

    Mar 15 11:14:14 gongzuo systemd[474]: Started Clipmenu daemon.
    % strace -p 9053
    strace: Process 9053 attached
    restart_syscall(<... resuming interrupted restart_syscall ...>^Cstrace: Process 9053 detached
     <detached ...>
    % ps aux | grep 9053
    cdown     9053  0.0  0.0  15956   896 ?        S    Mar15   0:00 xsel --logfile /dev/null -o --primary

clipmenud

@@ -7,7 +7,7 @@ lock_file=$cache_dir/lock
 lock_timeout=2
 
 _xsel() {
-    xsel --logfile /dev/null "$@"
+    timeout 1 xsel --logfile /dev/null "$@"
 }
 
 get_first_line() {