private void listadoMascotasToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (rptMasc == null)
     {
         rptMasc             = new frmRptMascotas();
         rptMasc.MdiParent   = this;
         rptMasc.FormClosed += new FormClosedEventHandler(rptMasc_FormClosed);
         rptMasc.Show();
     }
     else
     {
         rptMasc.Activate();
     }
 }
 void rptMasc_FormClosed(object sender, FormClosedEventArgs e)
 {
     rptMasc = null;
 }