completion: fix __git_complete_worktree_paths

Use __git to invoke "worktree list" in __git_complete_worktree_paths, to
respect any "-C" and "--git-dir" options present on the command line.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -3571,7 +3571,7 @@ __git_complete_worktree_paths ()
 	# Generate completion reply from worktree list skipping the first
 	# entry: it's the path of the main worktree, which can't be moved,
 	# removed, locked, etc.
-	__gitcomp_nl "$(git worktree list --porcelain |
+	__gitcomp_nl "$(__git worktree list --porcelain |
 		sed -n -e '2,$ s/^worktree //p')"
 }