Lisk-sdk: Inconsistent response for /transactions endpoint

[lsilvs]

Expected behavior

Given I make the following calls:

/transactions?blockId=:blockId&sort=timestamp:desc&offset=0&limit=51 and
/transactions?blockId=:blockId&sort=timestamp:desc&offset=50&limit=51

I expect the last item returned by the first call to be the same as the first item returned by the second call.

Actual behavior

It is not.

Steps to reproduce

Using the following test database:

Compare the first call with the second call

Which version(s) does this affect? (Environment, OS, etc...)

v1.0.0-beta.5

[diego-G]

Your calls are getting transactions with timestamp 0. What we need is a second default sort parameter as a tiebreaker.

[lsilvs]

Maybe it's a good idea to introduce this second default sort for all endpoints that have sorting option.