[Graph]: fix a bug in edge iterator for a general sparse matrix.
[Graph]: fix a bug in edge iterator for a general sparse matrix.

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