Change content check before overwriting cache

[coret]

The demonstrator get the creators, publishers and formats by doing a SPARQL query on the triplestore, the results are cached. Sometimes one of lists is empty in the user interface. A call to https://datasetregister.netwerkdigitaalerfgoed.nl/search.php with parameter ?nocache=1 make that the cache is skipped and the data is fetched from the source. Code should be changed that if there is no data for a specific SPARQL query returned, the cache should be left as is. The current check had that aim, but is not effective enough.

registry-demo/web/includes/search.php

Line 86 in 7bd1ceb

if (!empty($contents)) {

The check should be changed in something like that the $sparqlResults["results"]["bindings"] array has one or more elements.