[Graph]: fix a bug in constructing in-mem graph from edge lists.
[Graph]: fix a bug in constructing in-mem graph from edge lists.

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