firmware: logic analyzer: don't send an invalid first buffer
firmware: logic analyzer: don't send an invalid first buffer

greatscottgadgets/greatfet,dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental