If we are only searching for a price, don't try to match it as a term

If you search for only a price or price range (like $100-$200) you get no products.  This is because the code tried to add ```WHERE MATCH(terms) AGAINST ('$100-$200' IN BOOLEAN MODE)``` to the query.  The cause was that $boolean was set to ```$options['search']``` if it was empty.  I'm not sure the purpose of that exactly, and it might be the preferred treatment in some cases, so I left that alone.  Instead, a pricematch search is being done and the filtered search terms (after prices have been pulled out) are empty, I empty the WHERE clause completely (price matching happens in the having clause).