make tags lowercase before comparing them

[vinkaks]

Attempt to fix #3050. Issue results in a false error.

Issue is due to the applied tags vs user submitted tags check being case sensitive even though the database search used to generate applied tags is case insentitive.

[jiru]

Thanks for your PR! It appears the default collation makes varchar type case-insensitve by default, whereas the code assumes it is case-sensitve. Even though I didn’t know tags are case insensitive, we may want to keep it like this.

\App\Model\Search::filterByTags() is supposed to return the list of tags that have been successfully applied among the provided tags. Because that method is doing the SQL query, I think it would make more sense to have it handle the case thing, instead of its caller App\Form\SentencesSearchForm::setDataTags(). The caller shouldn’t have to deal with such implementation details. Can you try modifying filterByTags() in a way it works regardless of the case?