[R]: fix a bug in .agg.na.
[R]: fix a bug in .agg.na.

icoming/FlashX,flashxio/FlashX,icoming/FlashGraph,icoming/FlashGraph,icoming/FlashGraph,icoming/FlashX,flashxio/FlashX,icoming/FlashX,icoming/FlashX,flashxio/FlashX,icoming/FlashGraph,flashxio/FlashX,icoming/FlashGraph,flashxio/FlashX,icoming/FlashX,flashxio/FlashX