290. Validity of acts of directors. Acts done by a person as a director shall be valid, notwithstanding that it may afterwards be discovered that his appointment was invalid by reason of any defect or disqualification or had terminated by virtue of any provision contained in this Act or in the articles: Provided that nothing in this section shall be deemed to give validity to acts done by a director after his appointment has been shown to the company to be invalid or to have terminated. Board' s powers and restrictions thereon