line-log: initialize diff queue in process_ranges_ordinary_commit()

line-log: initialize diff queue in process_ranges_ordinary_commit()

process_ranges_ordinary_commit() uses a local diff queue variable,
which it leaves uninitialized before passing its address to
queue_diffs().  This is not an issue, because at the end of that
function the contents of an other diff queue is moved into it by
simply overwriting whatever is in there, i.e. without reading any
uninitialized memory.

Still, seeing the uninitialized diff queue being passed around scared
me more than once, so out of caution let's make sure that it's
initialized.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>