Don't fall thru to Hydra::View::NARInfo

This caused exceptions like:

Caught exception in Hydra::Controller::Build->view_build "writing to file: Broken pipe at /nix/store/ihdb3widsq1dk7sbl5vqjxfcxb5ypad4-hydra-0.1pre1297-8158093/libexec/hydra/lib/Hydra/Controller/Build.pm line 59."

because the connection to the Nix daemon would be terminated due to a protocol violation (calling queryPathInfo with an empty string).

Created by  Eelco Dolstra  on April 30, 2013
5OXBTB3LCJ7N4EKOLAPCRFNFH4IGFEAXWIP4WRM6G5OSCUIEDH2QC
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