private void textBox7_KeyPress(object sender, KeyPressEventArgs e)
 {
     if (textBox7.Text.Length == 0 && e.KeyChar == ' ')
     {
         e.KeyChar = (char)0;
     }
     else if (textBox7.Text.Length > 0 && e.KeyChar == (char)13)
     {
         Guardar.Focus();
     }
 }