gitk: Fix bug caused by missing commitlisted elements

gitk: Fix bug caused by missing commitlisted elements

This bug was reported by Yann Dirson, and results in an 'Error:
expected boolean value but got ""' dialog when scrolling to the bottom
of the graph under some circumstances.  The issue is that git-rev-list
isn't outputting all the boundary commits when it is asked for commits
affecting only certain files.  We already cope with that by adding the
missing boundary commits in addextraid, but there we weren't adding a
0 to the end of the commitlisted list when we added the extra id to
the end of the displayorder list.

This fixes it by appending 0 to commitlisted in addextraid, thus keeping
commitlisted and displayorder in sync.

Signed-off-by: Paul Mackerras <paulus@samba.org>