Though illegal votes be received, or legal votes be rejected, at any place of voting, the returns of the votes taken at such place shall not be set aside for that cause, but it may be shown, by proper evidence before the tribunal authorized by law to hear and determine contested elections, for whom such illegal votes or any of them were cast, or for whom the legal votes which were rejected would have been given, and the returns shall be corrected only to the extent that it is so shown.