updated fibergraph to preserve node structure when deleting zero
updated fibergraph to preserve node structure when deleting zero

openconnectome/m2g,neurodata/ndmg,openconnectome/m2g,neurodata/ndgrutedb,openconnectome/m2g,openconnectome/m2g,openconnectome/m2g,neurodata/ndgrutedb,neurodata/ndgrutedb,neurodata/ndgrutedb,neurodata/ndgrutedb,openconnectome/m2g,openconnectome/m2g,neurodata/ndgrutedb,neurodata/ndgrutedb,neurodata/ndgrutedb,openconnectome/m2g