[Graph]: fix memory leak in 2D triangle counting.
[Graph]: fix memory leak in 2D triangle counting.

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