private void BtnInventory_Click(object sender, EventArgs e)
 {
     if (frmInv == null || frmInv.IsDisposed)
     {
         frmInv = new frmInventory();
         frmInv.Show();
     }
 }
 private void BtnInventory_Click(object sender, EventArgs e)
 {
     frmInv = new frmInventory();
     frmInv.ShowDialog();
 }