private void listOfBookToolStripMenuItem_Click(object sender, EventArgs e)
        {
            frm_listOfBooks form = new frm_listOfBooks();

            try
            {
                form.Show();
            }
            catch (InvalidOperationException)
            {
                form.Show();
            }
        }
        private void listOfBooksToolStripMenuItem_Click(object sender, EventArgs e)
        {
            frm_listOfBooks form = new frm_listOfBooks();

            form.Show();
        }