[FIX] ODataModel: getLength should return 0 while refreshing

We recently made change to make getLength return an estimated length, if
the final length is not known yet. However this should only be done,
once the server returned data for the first time, not while waiting for
the initial response.

BCP: 0020079747 0001145175 2014
Change-Id: Icb09c45f51e9c71b109b255df38d5293363e29c9
Merge "[FIX] ODataModel: getLength should return 0 while refreshing"