Adding early return if the cell is filled with a material.
Adding early return if the cell is filled with a material.

amandalund/openmc,paulromano/openmc,walshjon/openmc,shikhar413/openmc,mit-crpg/openmc,mit-crpg/openmc,amandalund/openmc,mit-crpg/openmc,shikhar413/openmc,paulromano/openmc,smharper/openmc,liangjg/openmc,amandalund/openmc,liangjg/openmc,smharper/openmc,amandalund/openmc,smharper/openmc,paulromano/openmc,walshjon/openmc,liangjg/openmc,paulromano/openmc,shikhar413/openmc,liangjg/openmc,smharper/openmc,walshjon/openmc,shikhar413/openmc,walshjon/openmc,mit-crpg/openmc