Reset status on empty commands.

* gash/eval.scm (exp->thunk, exps->thunk): When the expression has
value '#f', reset the status.

gash/eval.scm

@@ -59,7 +59,7 @@
   ;; XXX: See comment in `exps->thunk'.
   (if exp
       (lambda () (eval-sh exp))
-      noop))
+      (lambda () (set-status! 0))))
 
 (define (exps->thunk exps)
   ;; XXX: It probably makes more sense to exclude '#f' expressions at
@@ -68,7 +68,7 @@
       (match (filter values exps)
         (() noop)
         (exps (lambda () (eval-sh `(<sh-begin> ,@exps)))))
-      noop))
+      (lambda () (set-status! 0))))
 
 (define (eval-sh exp)
   "Evaluate the Shell expression @var{exp}."