Return '' from getTokenSalt to enable token check

If getTokenSalt is not overwritten, it returns false,
disabling the token check in ApiMain. We forget about
this, but I don't think this was a big issue, since we
do our own token check in EditEntity (not the API module)
anyway.

Change-Id: I9395b65473167a205fb1970f5232b36a9a26bdd6
Merge "Return '' from getTokenSalt to enable token check"