[BUGFIX] Repository uses wrong property to calc current result page

In the IndexedSearchRepository on line 157 an undefined/unused 
property $this->resultsPerPage is used for the calculation 
of the current page the visitor is showing on search results.

Instead of using $this->resultsPerPage we have to use 
$this->numberOfResults which is defined and contains the expected setting.

Change-Id: I37c3a08c1049eb6166704b2b98ba071f03aad243
Resolves: #54808
Releases: 6.2, 6.1
Reviewed-on: https://review.typo3.org/26678
Reviewed-by: Markus Klein
Tested-by: Markus Klein