mongo-sync: Fix _cmd_query() to return FALSE on no results.
mongo-sync: Fix _cmd_query() to return FALSE on no results.

When there are no results, return FALSE and set errno to ENOENT. In
case of a server-side query fail, set errno to EPROTO instead.

algernon/libmongo-client,algernon/libmongo-client,algernon/libmongo-client