[balsa] main-window: Do not leak GError

[Peter Bloomfield <peterb src gnome org>]

commit ba8f912a4b78c82c5b0ba98214105b6373c8c2d2
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Mon Mar 29 10:38:46 2021 -0400

    main-window: Do not leak GError
    
    in bw_real_open_mbnode_thread().

 src/main-window.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/main-window.c b/src/main-window.c
index 49ea98d6f..e20a90b56 100644
--- a/src/main-window.c
+++ b/src/main-window.c
@@ -2982,6 +2982,8 @@ bw_real_open_mbnode_thread(BalsaWindowRealOpenMbnodeInfo * info)
             LIBBALSA_INFORMATION_ERROR,
             _("Unable to Open Mailbox!\n%s."),
            err ? err->message : _("Unknown error"));
+        if (err != NULL)
+            g_error_free(err);
         balsa_window_decrease_activity(info->window, info->message);
         bw_open_mbnode_info_free(info);
     }