[ALF-22050] CQ: Allow to recover empty pagings

[tartard]

Requesting a paging wich does not exist should return either null, either an empty paging which can give the information on the absence of results.
Currently, the only way to know the number of results in a PagingResult is to call PagingResults#getPage() .
The problem is that this method throws an exception if the paging has no results when asking an out-of-bound page (for example asking for page two with 10 items in a query which has only 9 results).

Even if most of the time the developer has control over the paging of his request, it is not fundamentally wrong to ask for a not existing paging. It is like making a query which has no results, and in this case no exception is raised.

[killerboot]

@tartard Thanks for the fix.
Could you please rebase against latest master, it has Travis config. So that we can see the test results here.

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[tartard]

@killerboot , sorry I didn't notice your comment almost 2 years ago... I just updated my PR by rebasing against the latest master. I hope it is still ok.