fix leak in tests (#714)
fix leak in tests (#714)

coverity cid: 116836
jmikola/mongo-c-driver,jmikola/mongo-c-driver,beingmeta/mongo-c-driver,mongodb/mongo-c-driver,beingmeta/mongo-c-driver,beingmeta/mongo-c-driver,jmikola/mongo-c-driver,rcsanchez97/mongo-c-driver,rcsanchez97/mongo-c-driver,beingmeta/mongo-c-driver,jmikola/mongo-c-driver,mongodb/mongo-c-driver,jmikola/mongo-c-driver,beingmeta/mongo-c-driver,beingmeta/mongo-c-driver,jmikola/mongo-c-driver,rcsanchez97/mongo-c-driver,jmikola/mongo-c-driver,rcsanchez97/mongo-c-driver,rcsanchez97/mongo-c-driver,mongodb/mongo-c-driver,rcsanchez97/mongo-c-driver,mongodb/mongo-c-driver,mongodb/mongo-c-driver,rcsanchez97/mongo-c-driver,beingmeta/mongo-c-driver,mongodb/mongo-c-driver,beingmeta/mongo-c-driver,mongodb/mongo-c-driver