FIX: Re-added reference-property filtering.

For issue #110

src/main/java/org/caosdb/server/query/Backreference.java

@@ -214,6 +214,7 @@ public class Backreference implements EntityFilterInterface, QueryInterface {
           this.statistics.put(
               "subPropertySourceSetCount", Utils.countTable(query.getConnection(), this.sourceSet));
           this.targetSet = null;
+          getSubProperty().getFilter().apply(this);
 
           final long t3 = System.currentTimeMillis();
           try (final PreparedStatement callFinishSubProperty =