merge-ort: fix slightly overzealous assertion for rename-to-self

merge-ort: fix slightly overzealous assertion for rename-to-self

merge-ort has a number of sanity checks on the file it is processing in
process_renames().  One of these sanity checks was slightly overzealous
because it indirectly assumed that a renamed file always ended up at a
different path than where it started.  That is normally an entirely fair
assumption, but directory rename detection can make things interesting.

As a quick refresher, if one side of history renames directory A/ -> B/,
and the other side of history adds new files to A/, then directory
rename detection notices and suggests moving those new files to B/.  A
similar thing is done for paths renamed into A/, causing them to be
transitively renamed into B/.  But, if the file originally came from B/,
then this can end up causing a file to be renamed back to itself.

It turns out the rest of the code following this assertion handled the
case fine; the assertion was just an extra sanity check, not a rigid
precondition.  Therefore, simply adjust the assertion to pass under this
special case as well.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>