Merge branch 'jk/proto-v2-ref-prefix-fix'

"git fetch" over protocol v2 sent an incorrect ref prefix request
to the server and made "git pull" with configured fetch refspec
that does not cover the remote branch to merge with fail, which has
been corrected.

* jk/proto-v2-ref-prefix-fix:
  fetch: add branch.*.merge to default ref-prefix extension
  fetch: stop checking for NULL transport->remote in do_fetch()

diff --cc builtin/fetch.c
Simple merge