Appeals — Certiorari — Discovery orders — Blanket order denying without prejudice a motion to compel depositions of 18 witnesses who were alleged to be material and contemporaneously granting protective order, without addressing materiality of any of the deponents or finding good cause to preclude depositions, constituted departure from essential requirements of law causing material injury for which there is no adequate remedy at law — Fact that order was without prejudice to petitioners refiling another motion to compel does not change result