MB-24976: Avoid infinite loop in calcPartialCompactionStart
MB-24976: Avoid infinite loop in calcPartialCompactionStart

If the incoming data size is 0 for some reason, the determineExponent()
runs into an infinite loop. Fix by testing for 0.

Change-Id: I0e8347634b44674ff76880b74bbc5a7833747291
Reviewed-on: http://review.couchbase.org/79851
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Tested-by: Sundararaman Sridharan <333a3f71d3ad6e01fc953c4fa06bc1f3cd014910@couchbase.com>

couchbaselabs/moss,steveyen/moss,steveyen/moss