A shareholder in a limited company who is also a creditor of the company under a contract is not, in the event of the company being wound up, entitled to set off the debt due to him as against the calls, but on payment of the amount of all calls that become due, he is entitled to receive dividends at the same time and at the same rate as other creditors of the company; but, if the contributory has himself become insolvent, he may so set off the debt due to him against the calls, inasmuch as in insolvency mutual debts may be set off one against the other. If, however, he has not yet become insolvent, but the company is endeavouring to make him insolvent as for non-payment of the calls, he is not entitled to set off the debt due to him against the petitioning creditor’s debt.