Fix a SEGFAULT in 'fs-test --fs-type=bdb 36'.
Fix a SEGFAULT in 'fs-test --fs-type=bdb 36'.

* subversion/libsvn_fs_base/obliterate.c
  (svn_fs_base__node_rev_dup): Only attempt to dup file content
    representations when they actually exist.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@890951 13f79535-47bb-0310-9956-ffa450edef68

wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion