offline editing: keep subset filter (hello from FOSSGIS)

src/core/qgsofflineediting.cpp

@@ -602,7 +602,7 @@ QgsVectorLayer* QgsOfflineEditing::copyVectorLayer( QgsVectorLayer* layer, sqlit
       QgsFeature f;
 
       // NOTE: force feature recount for PostGIS layer, else only visible features are counted, before iterating over all features (WORKAROUND)
-      layer->setSubsetString( "" );
+      layer->setSubsetString( layer->subsetString() );
 
       QgsFeatureIterator fit = layer->dataProvider()->getFeatures();