SolrSearch: Inconsistent search results for documents with or without attachment

Ticket based on discussion https://forum.xwiki.org/t/no-attachments-appear-in-search-results/8770/6

Steps to reproduce:

1. Replace SolrSearchConfig with file attached - I removed attachment criteries from DOCUMENT fields
2. Import pages from ticket attachment documentsearchtest.xar
3. Make a local search in this pages for "ramalamadingdong" (without quotes) - you can use the local search embedded in the page DocumentSearchTest
4. Check search results. You get 2 results, which is correct (for the 2 sub pages with the keyword in den document content.
5. Remove the checkmark from result type DOCUMENT in the facets right (so you get document and attachment results)

Actual result:

The number of results for result type DOCUMENT is suddenly 3.
The page "DocumentSearchTest - OnlyAttachment" is shown as result.

Expected result:

The numer of results for type DOCUMENT should still be 2.
The page "DocumentSearchTest - OnlyAttachment" should not be shown, because it results from an attachment and my change in SolrSearchConfig excludes attachments from document searches.