Apply collection query constraint/modifiert to rwi result stack.

Collection is not available in pure rwi entries (but in local solr metadata)
But if user wishes to filter by query constraint also rwi shall adhere to this
(even if only rwi entries with parsed or solr received metadata may fit)

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

@@ -1159,6 +1159,9 @@ public final class SearchEvent {
                 continue;
             }
 
+            // filter query modifiers variables (these are host, filetype, protocol, language, author, collection, dates_in_content(on,from,to,timezone) )
+            // while ( protocol, host, filetype ) currently maybe incorporated in (this.query.urlMaskPattern)  queryparam
+
             // check modifier constraint filetype (using fileextension)
             if (this.query.modifier.filetype != null && !this.query.modifier.filetype.equals(ext)) {
                 if (log.isFine()) log.fine("dropped RWI: file type constraint = " + this.query.modifier.filetype);
@@ -1180,7 +1183,20 @@ public final class SearchEvent {
                 if (page.word().local()) this.local_rwi_available.decrementAndGet(); else this.remote_rwi_available.decrementAndGet();
                 continue;
             }
-            
+
+            // check modifier constraint collection
+            // this is not available in pure RWI entries (but in local or via solr query received metadate/entries), 
+            if (this.query.modifier.collection != null) {
+                Collection<Object> docCols = page.getFieldValues(CollectionSchema.collection_sxt.getSolrFieldName()); // get multivalued value
+                if (docCols == null) { // no collection info
+                    if (page.word().local()) this.local_rwi_available.decrementAndGet(); else this.remote_rwi_available.decrementAndGet();
+                    continue;
+                } else if (!docCols.contains(this.query.modifier.collection)) {
+                    if (page.word().local()) this.local_rwi_available.decrementAndGet(); else this.remote_rwi_available.decrementAndGet();
+                    continue;
+                }
+            }
+
             // Check for blacklist
             if (Switchboard.urlBlacklist.isListed(BlacklistType.SEARCH, page.url())) {
                 if (log.isFine()) log.fine("dropped RWI: url is blacklisted in url blacklist");
@@ -1252,7 +1268,7 @@ public final class SearchEvent {
                 continue;
             }
             
-          
+                
             // check vocabulary terms (metatags) {only available in Solr index as vocabulary_xxyyzzz_sxt field}
             // TODO: vocabulary is only valid and available in local Solr index (consider to auto-switch to Searchdom.LOCAL)
             if (this.query.metatags != null && !this.query.metatags.isEmpty()) {