Local fix to SCons bug:
Local fix to SCons bug:

If a Node exists explicitly in a repository directory but not in the
local working directory, SCons would throw an exception when globbing
the entry when it tried to extract the non-existent same-named entry
from the local working directory's entries dictionary.  Since we know
we want to return local entry anyway, make sure it exists.
Review URL: http://codereview.chromium.org/13044

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@6212 0039d316-1c4b-4281-b951-d872f2087c98

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