work around zsh comment in __git_complete_worktree_paths

work around zsh comment in __git_complete_worktree_paths

[PATCH]: contrib/completion/git-completion.bash, there is a construct
where comment lines are placed between the command that is on
the upstream of a pipe and the command that is on the downstream
of a pipe in __git_complete_worktree_paths function.

Unfortunately, this script is also used by Zsh completion, but
Zsh mishandles this construct when "interactive_comments" option is not
set (by default it is off on macOS), resulting in a breakage:

$ git worktree remove [TAB]
$ git worktree remove __git_complete_worktree_paths:7: command not found: #

Move the comment, even though it explains what happens on the
downstream of the pipe and logically belongs where it is right
now, before the entire pipeline, to work around this problem.

Signed-off-by: Sardorbek Imomaliev <sardorbek.imomaliev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>