When finishing the current section some index records might be written
for the section to the table. The logic that adds these records to the
writer duplicates what we already have in `writer_add_record()`, making
this more complicated than it really has to be.
Simplify the code by using `writer_add_record()` instead. While at it,
drop the unneeded braces around a loop to make the code conform to our
code style better.
Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>