[ghex/gtk4-port: 86/91] Fix assertion error when quitting with file open

[Logan Rathbone <larathbone src gnome org>]

commit a31c7608e66ee6e45b9916ccd4e7034603a4958f
Author: Logan Rathbone <poprocks gmail com>
Date:   Thu Aug 5 09:50:14 2021 -0400

    Fix assertion error when quitting with file open

 src/ghex-application-window.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/ghex-application-window.c b/src/ghex-application-window.c
index 027192c7..fc6011ae 100644
--- a/src/ghex-application-window.c
+++ b/src/ghex-application-window.c
@@ -879,8 +879,10 @@ ghex_application_window_set_show_ ##WIDGET (GHexApplicationWindow *self,   \
        }                                                                                                     
                                          \
        else                                                                                                  
                                  \
        {                                                                                                     
                                          \
-               if (gtk_widget_is_visible (self->WIDGET))                                                     
  \
+               if (GTK_IS_WIDGET (self->WIDGET) &&                                                           
          \
+                               gtk_widget_is_visible (self->WIDGET)) {                                       
  \
                        gtk_widget_hide (self->WIDGET);                                                       
          \
+               }                                                                                             
                                          \
        }                                                                                                     
                                          \
        g_object_notify_by_pspec (G_OBJECT(self), properties[PROP_ARR_ENTRY]);  \
 }                                                                                              /* 
DIALOG_SET_SHOW_TEMPLATE */