In a case tried before a jury, the court on motion of the defendant or on its own motion, at the close of the evidence on either side and before the case is submitted to the jury for decision, shall order the entry of a judgment of acquittal of one or more of the offenses charged in the accusatory pleading if the evidence then before the court is insufficient to sustain a conviction of such offense or offenses on appeal. If such a motion for judgment of acquittal at the close of the evidence offered by the prosecution is not granted, the defendant may offer evidence without first having reserved that right.