[mutter] keybinding: Check for handler functions as well

[Olivier Fourdan <ofourdan src gnome org>]

commit 76f2579e442d8ad0a3b8b644daab7c72a585506b
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Tue Sep 24 16:58:32 2019 +0200

    keybinding: Check for handler functions as well
    
    With the addition of the locate-pointer special keybinding (defaults to
    the [Control] key), we have now two separate special modifier keys which
    can be triggered separately, one for the locate-pointer action and
    another one for overlay.
    
    When processing those special modifier keys, mutter must ensure that the
    key was pressed alone, being a modifier, the key could otherwise be part
    of another key combo.
    
    As result, if both special modifiers keys are pressed simultaneously,
    mutter will try to trigger the function for the second key being
    pressed, and since those special modifier keys have no default handler
    function set, that will crash mutter.
    
    Check if the handler has a function associated and treat the keybinding
    as not found if no handler function is set, as with the special modifier
    keys.
    
    https://gitlab.gnome.org/GNOME/mutter/issues/823

 src/core/keybindings.c | 9 +++++++++
 1 file changed, 9 insertions(+)
---
diff --git a/src/core/keybindings.c b/src/core/keybindings.c
index b9377bfff..b86272541 100644
--- a/src/core/keybindings.c
+++ b/src/core/keybindings.c
@@ -1933,6 +1933,12 @@ invoke_handler (MetaDisplay     *display,
                                NULL);
 }
 
+static gboolean
+meta_key_binding_has_handler_func (MetaKeyBinding *binding)
+{
+  return (!!binding->handler->func || !!binding->handler->default_func);
+}
+
 static gboolean
 process_event (MetaDisplay          *display,
                MetaWindow           *window,
@@ -1958,6 +1964,9 @@ process_event (MetaDisplay          *display,
   if (binding->handler == NULL)
     meta_bug ("Binding %s has no handler\n", binding->name);
 
+  if (!meta_key_binding_has_handler_func (binding))
+    goto not_found;
+
   if (display->focus_window &&
       !(binding->handler->flags & META_KEY_BINDING_NON_MASKABLE))
     {