ui/gtk: fix crash at startup when no console is available

This patch fixes a segfault at QEMU startup, introduced in a0815632.
gd_vc_find_current() return NULL, which is dereferenced without checking it.

While at it, disable the whole 'View' menu if no console exists.

Reproducer: qemu-system-i386 -M none -nodefaults
Signed-off-by: NHervé Poussineau <hpoussin@reactos.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 1483263585-8101-1-git-send-email-hpoussin@reactos.org
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/gtk.c

@@ -2171,6 +2171,8 @@ static gboolean gtkinit;
 
 void gtk_display_init(DisplayState *ds, bool full_screen, bool grab_on_hover)
 {
+    VirtualConsole *vc;
+
     GtkDisplayState *s = g_malloc0(sizeof(*s));
     char *filename;
     GdkDisplay *window_display;
@@ -2249,9 +2251,11 @@ void gtk_display_init(DisplayState *ds, bool full_screen, bool grab_on_hover)
     }
 #endif
 
+    vc = gd_vc_find_current(s);
+    gtk_widget_set_sensitive(s->view_menu, vc != NULL);
 #ifdef CONFIG_VTE
     gtk_widget_set_sensitive(s->copy_item,
-                             gd_vc_find_current(s)->type == GD_VC_VTE);
+                             vc && vc->type == GD_VC_VTE);
 #endif
 
     if (full_screen) {