line-log: fix several memory leaks

line-log: fix several memory leaks

As described in "line-log.c" itself, the code is "leaking like a sieve".
These leaks are all of rather trivial nature, so this commit plugs them
without going too much into details for each of those leaks.

The leaks are hit by t4211, but plugging them alone does not make the
full test suite pass. The remaining leaks are unrelated to the line-log
subsystem.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>