If more than three challenges to individual grand jurors are allowed to the same defendant in reference to the same charge, the court must fill the panel to sixteen as to that charge by causing a sufficient number of competent jurors from those summoned and not before called, or if a sufficient number are not in attendance, then from the bystanders or from the body of the county to be sworn to act as jurors with the regular panel, upon the examination of that charge; and, if necessary to secure the full number of sixteen competent jurors, the court may require the sheriff to summon the required number.