Right now, the ToC has an undefined variable i that was an index in the
original ToC code. Since the major rewrite in
4fe0620853 it's a recursive function
without this index. The variable `i` was wrongly copied into its current
place from the old code.
This patch replaces the variable `i` with the index of the header
element. Fix the undefined variable problem.
Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>