Calling empty std::function behaves different than calling empty Link

...regression introduced with a50cd187 "make
Control::ImplCallEventListenersAndHandler take a lambda"

Change-Id: I62e66d71cd36e55d68cf15c70dc9e06214f7e312

vcl/source/control/ctrl.cxx

@@ -328,7 +328,10 @@ bool Control::ImplCallEventListenersAndHandler( sal_uLong nEvent, std::function<
 
     if ( !xThis->IsDisposed() )
     {
-        callHandler();
+        if (callHandler)
+        {
+            callHandler();
+        }
 
         if ( !xThis->IsDisposed() )
             return false;