scripts/finish: do not try to symlink if sed expr is a no-op

If the sed expression does not transform the
tuple, do not try to create the symlink.
(transplanted from 5d6d3c28a658a65551d4eb5de414fd97b575f314)

 reporter_name="Bart vd. Meulen"

 reporter_url=""

 reporter_comment="Sample for building a canadian cross-compiler"