[balsa/gtk4: 290/314] sendmsg-window: GtkWindow is not a GtkBox

[Peter Bloomfield <peterb src gnome org>]

commit 7d2e6a8feacd0630d40413e526592bb7c4e0d575
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Sat Nov 21 12:48:11 2020 -0500

    sendmsg-window: GtkWindow is not a GtkBox

 src/sendmsg-window.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/sendmsg-window.c b/src/sendmsg-window.c
index 6bc9fda6e..6dda24126 100644
--- a/src/sendmsg-window.c
+++ b/src/sendmsg-window.c
@@ -7362,7 +7362,7 @@ sendmsg_window_new()
         gtk_application_window_new(balsa_app.application);
     geometry_manager_attach(GTK_WINDOW(window), "SendMsgWindow");
 
-    gtk_box_append(GTK_BOX(window), main_box);
+    gtk_window_set_child(GTK_WINDOW(window), main_box);
     gtk_widget_show(window);
 
     bsmsg->gpg_mode = LIBBALSA_PROTECT_RFC3156;