[balsa/wip/gtk4] Fix the build

[Peter Bloomfield <peterb src gnome org>]

commit f379f5aef3acfcbb05a275753082d26527778a94
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Wed May 30 16:54:40 2018 -0400

    Fix the build

 src/balsa-index.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/balsa-index.c b/src/balsa-index.c
index 8f2fe6adc..524b5b45f 100644
--- a/src/balsa-index.c
+++ b/src/balsa-index.c
@@ -1697,7 +1697,7 @@ bndx_compose_foreach(BalsaIndex *index,
         }
 
         if (sm != NULL) {
-            g_signal_connect(G_OBJECT(sm->window), "destroy",
+            g_signal_connect(sendmsg_window_get_window(sm), "destroy",
                              G_CALLBACK(sendmsg_window_destroy_cb), NULL);
         } else {
             ++skipped;