Making it so when no search occurs, 'no results' is not *always* thrown.

[JoshKoberstein]

When no search is occurring, the plugin should optionally throw a 'no results' response because always doing so causes conflict with other channel:entries parameters.

For instance, say we have the following code:
{exp:search_fields search:title="{document_route_keywords}" required="n" no_results="y" search:document_content="{document_route_keywords}" search:document_document_excerpt="{document_route_keywords}" operator="OR" channel="document" parse="inward"} {exp:channel:entries entry_id="{search_results}" channel="document" status="open" dynamic="no" paginate="bottom" limit="5" category="{document_route_category_ids}"}
`

This is code for a documents section that is filterable by keyword and multiple document category groups.

If there are no keywords present ( {document_route_keywords} ), no_results will be returned. However, I may still want to view documents of a certain category.

I added a 'required' parameter to specify whether or not performing a search is required. If required and no search parameters are present, no_results will be set to true. If not required and no search parameters are present, the placeholder variable will be set to a blank string so that additional channel entries loop parameters will be processed.