Error checking: GtkSpell Reference Manual

## Error checking

`gtk_spell_checker_set_language` returns `FALSE` if there was an error. If a `GError **` was provided as the last argument, the error message can be displayed to the user:

    GError *err = NULL; /* this initialization is important. */
    /* ... */
    GtkSpellChecker* spell = gtk_spell_checker_new ();
    if (!gtk_spell_checker_set_language (spell, "en_US", &err))
      {
        GtkWidget *errdlg;
        errdlg = gtk_message_dialog_new (main_application_window,
                                         GTK_DIALOG_DESTROY_WITH_PARENT,
                                         GTK_MESSAGE_ERROR,
                                         GTK_BUTTONS_CLOSE,
                                         "Error initializing spell checking: %s",
                                         err->message);
                                         gtk_dialog_run (GTK_DIALOG (errdlg));
      gtk_widget_destroy (errdlg);
      g_error_free (err); /* don't forget to free GErrors when you're done! */
      }