if last_row is present in remote data, don't require last_page

[liedekef]

Is your feature request related to a problem? Please describe.
Currently, for paging, the remote side needs to give at least last_page and for correctness also last_row.
This means a php-solution that gets info from mysql needs to get the count (last_row) and then calculate the total amount of pages too.

Describe the solution you'd like
Most table-solutions require only the total record count (last_row), and when that is present, last_page can be calculated in javascript.
Since in php all solutions do a count(*) to get the total rows, it is more logical to set last_row than to also need to do the page calc on server side.
I've verified that last_page is only used in _parseRemoteData and can be calculated if last_row is present. This is about 5 lines of code-change :-)