[BUGFIX] Ensure proper items per page setting

If Solr is initialized with an empty query (initializeWithEmptyQuery)
usedResultsPerPage is empty and will lead to an exception. To avoid
this the default configuration from TypoScript is used.

Resolves: TYPO3-Solr#3150

Classes/Controller/SearchController.php

@@ -114,7 +114,7 @@ public function resultsAction(): ResponseInterface
             $this->controllerContext->setSearchResultSet($searchResultSet);
 
             $currentPage = $this->request->hasArgument('page') ? (int)$this->request->getArgument('page') : 1;
-            $itemsPerPage = $searchResultSet->getUsedResultsPerPage();
+            $itemsPerPage = ($searchResultSet->getUsedResultsPerPage() ?: $this->typoScriptConfiguration->getSearchResultsPerPage(10));
             $paginator = GeneralUtility::makeInstance(ResultsPaginator::class, $searchResultSet, $currentPage, $itemsPerPage);
             $pagination = GeneralUtility::makeInstance(ResultsPagination::class, $paginator);
             $pagination->setMaxPageNumbers((int)$this->typoScriptConfiguration->getMaxPaginatorLinks(0));