Merge branch 'kj/refspec-parsing-outside-repository'

Merge branch 'kj/refspec-parsing-outside-repository'

"git ls-remote '+refs/tags/*:refs/tags/*' https://..." run outside a
repository would dereference a NULL while trying to see if the given
refspec is a single-object refspec, which has been corrected.

* kj/refspec-parsing-outside-repository:
  refspec: fix typo in comment
  remote-curl: fall back to default hash outside repo