allow unwind_action functions to be empty and set after object creation * unwind-prot.h (unwind_action::unwind_action): New overload that allows unwind_action to be created without a valid function. (unwind_action::set): New functions. Allow action to be changed or set to an invalid function. (unwind_action::run): New function. Skip action if it is invalid. (unwind_action::~unwind_action): Use run to execute action.

--- a/liboctave/util/action-container.h	Sun Jan 03 20:19:04 2021 +0100
+++ b/liboctave/util/action-container.h	Sun Jan 03 14:37:13 2021 -0500
@@ -70,6 +70,9 @@
     {
     public:
 
+      // FIXME: Do we need to apply std::forward to the arguments to
+      // std::bind here?
+
       template <typename F, typename... Args>
       fcn_elem (F&& fcn, Args&&... args)
         : m_fcn (std::bind (fcn, args...))