Fix issue 1674: "svnadmin load" crashes on contentful rev 0.
Fix issue 1674: "svnadmin load" crashes on contentful rev 0.

* subversion/libsvn_repos/load.c (new_node_record): Fail gracefully if a node
    record is found in revision 0 of a dumpstream.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion