WebSearch: search results pattern limit fix

• Fixes pattern-limit style of queries (/search?subject=physics) by modifying prs_apply_search_limits so that the results_final dictionary is updated, rather than re-defined locally. (closes #1750) (PR #1751)

Signed-off-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
Co-authored-by: Ludmila Marian <ludmila.marian@gmail.com>
Tested-by: Tibor Simko <tibor.simko@cern.ch>