Handle indirect repos - set tags to empty.

I've updated the code to set tags to NULL/empty when the repo is indirect.

I've done this by looking at the sub-directories for the file - if the highest sub-directory is ```.git``` then we must be in an indirect repo.

i.e. an indirect filename looks something like:

    /home/me/annex-photos/.git/annex/objects/gX/Z3/SHA256E-<blah>.jpg/SHA256E-<blah>.jpg

So the top sub-directory here is ```.git```