unpack-trees: use 'cuddled' style for if-else cascade

unpack-trees: use 'cuddled' style for if-else cascade

Match the predominant style in git by following K&R style for if/else
cascades.  Documentation/CodingStyle from linux.git explains:

  Note that the closing brace is empty on a line of its own, _except_ in
  the cases where it is followed by a continuation of the same statement,
  ie a "while" in a do-statement or an "else" in an if-statement, like
  this:

	if (x == y) {
		..
	} else if (x > y) {
		...
	} else {
		....
	}

  Rationale: K&R.

  Also, note that this brace-placement also minimizes the number of empty
  (or almost empty) lines, without any loss of readability.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>