xbps_rpool_foreach: take into account xbps_repo_open returning NULL.
xbps_rpool_foreach: take into account xbps_repo_open returning NULL.

datenwolf/xbps,datenwolf/xbps,stpx/xbps,ebfe/xbps,ebfe/xbps,ebfe/xbps,stpx/xbps,stpx/xbps,datenwolf/xbps