Fix bug caused buf to be shared across threads
Fix bug caused buf to be shared across threads

jsbattig/mongo-c-driver,eugene-convey/mongo-c-driver,jsbattig/mongo-c-driver,Convey-Compliance/mongo-c-driver,Convey-Compliance/mongo-c-driver,Convey-Compliance/mongo-c-driver,eugene-convey/mongo-c-driver,eugene-convey/mongo-c-driver,Convey-Compliance/mongo-c-driver,Convey-Compliance/mongo-c-driver,jsbattig/mongo-c-driver