Websearch: fix results when applying search limits

* Fixes prs_apply_search_limits so that the results_final dictionary is
  updated, rather than re-defined locally.

(closes #1750)

Signed-off-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
Co-Authored-By: Ludmila Marian <ludmila.marian@gmail.com>
Merge pull request #41 from kasioumis/master-search-engine-fix-apply-search-limits

Websearch: fix results when applying search limits