setdiscovery: return anyincoming=False when remote's only head is nullid This fixes (issue2907) a crash when using 'hg incoming --bundle' with an empty remote repo and a non-empty local repo. This also fixes an unreported bug that 'hg summary --remote' erroneously reports incoming changes when the remote repo is empty and the local is not. Also, add a test to make sure issue2907 stays fixed

Minimal hgk check

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "hgk=" >> $HGRCPATH
  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ hg debug-cat-file commit 0
  tree a0c8bcbbb45c
  parent 000000000000
  author test 0 0
  committer test 0 0
  revision 0
  branch default
  
  adda