Bug 748983 - Crash after opening money transfer dialog twice

Prevent re-entrance by checking that the static pointers, the second
freeing of which caused the crash. Set said pointers to NULL after
freeing them to make the dialog ready for the next invocation.

src/gnome-utils/dialog-transfer.c

@@ -1871,6 +1871,7 @@ gnc_xfer_dialog_create(GtkWidget *parent, XferDialog *xferData)
 {
     GtkBuilder *builder;
     gboolean  use_accounting_labels;
+    g_return_if_fail(to_info == NULL && from_info == NULL);
 
     use_accounting_labels = gnc_prefs_get_bool(GNC_PREFS_GROUP_GENERAL,
                                                GNC_PREF_ACCOUNTING_LABELS);
@@ -2067,7 +2068,9 @@ close_handler (gpointer user_data)
     gnc_xfer_dialog_close_cb(GTK_DIALOG(dialog), xferData);
     gtk_widget_destroy (dialog);
     g_free (to_info);
+    to_info = NULL;
     g_free (from_info);
+    from_info = NULL;
     LEAVE(" ");
 }