[nautilus] Don't crash if parent button_press_event is NULL (#582457)

[Alexander Larsson <alexl src gnome org>]

commit 5fde2c7156b5bb8c0411bdbe649dd08172853d3a
Author: Alexander Larsson <alexl redhat com>
Date:   Wed May 13 13:41:45 2009 +0200

    Don't crash if parent button_press_event is NULL (#582457)
    
    This fixes a crash when you press on the empty area of the toolbars.
---
 src/nautilus-navigation-window.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/nautilus-navigation-window.c b/src/nautilus-navigation-window.c
index 04d0073..f698dfc 100644
--- a/src/nautilus-navigation-window.c
+++ b/src/nautilus-navigation-window.c
@@ -991,18 +991,20 @@ nautilus_navigation_window_button_press_event (GtkWidget *widget,
 {
 	NautilusNavigationWindow *window;
 	gboolean handled;
-	
+
 	handled = FALSE;
 	window = NAUTILUS_NAVIGATION_WINDOW (widget);
-	
+
 	if (mouse_extra_buttons && (event->button == mouse_back_button)) {
 		nautilus_navigation_window_go_back (window);
 		handled = TRUE; 
 	} else if (mouse_extra_buttons && (event->button == mouse_forward_button)) {
 		nautilus_navigation_window_go_forward (window);
 		handled = TRUE;
-	} else {
+	} else if (GTK_WIDGET_CLASS (nautilus_navigation_window_parent_class)->button_press_event) {
 		handled = GTK_WIDGET_CLASS (nautilus_navigation_window_parent_class)->button_press_event (widget, event);
+	} else {
+		handled = FALSE;
 	}
 	return handled;
 }