add content_type:image/* to image search

- see numerous idx entries with content_type image without url_file_ext_s (for various reason) which should be included in result
- try it yourself with following sample query
   /solr/select?q=content_type:image/* AND -url_file_ext_s:[* TO *]&defType=edismax&fl=sku,url_file_ext_s,content_type

adresses also possible url without or deviating extension.

source/net/yacy/search/query/QueryGoal.java

@@ -242,7 +242,8 @@ public class QueryGoal {
         // add filter to prevent that results come from failed urls
         q.append(CollectionSchema.httpstatus_i.getSolrFieldName()).append(":200").append(" AND (");
         q.append(CollectionSchema.images_urlstub_sxt.getSolrFieldName()).append(":[* TO *] OR ");
-        q.append(CollectionSchema.url_file_ext_s.getSolrFieldName()).append(":(jpg OR png OR gif))");
+        q.append(CollectionSchema.url_file_ext_s.getSolrFieldName()).append(":(jpg OR png OR gif) OR");
+        q.append(CollectionSchema.content_type.getSolrFieldName()).append(":(image/*))");
         
         // parse special requests
         if (isCatchall()) return q;