[SAFS]: fix a minor bug in in-mem IO.
[SAFS]: fix a minor bug in in-mem IO.

flashxio/FlashX,icoming/FlashX,zheng-da/FlashX,flashxio/FlashX,icoming/FlashX,flashxio/FlashX,flashxio/FlashX,flashxio/FlashX,icoming/FlashGraph,icoming/FlashX,flashxio/FlashX,zheng-da/FlashX,zheng-da/FlashX,icoming/FlashGraph,icoming/FlashGraph,icoming/FlashGraph,icoming/FlashGraph,icoming/FlashX,icoming/FlashX,zheng-da/FlashX,zheng-da/FlashX