vector file writer: scan shape file geometries instead of just assuming multi geometry types (followup 528c4ca, refs #10584, fixes #11542, fixes #11597)

Author: jef-n

src/core/qgsvectorfilewriter.cpp

@@ -1869,7 +1869,20 @@ QgsVectorFileWriter::WriterError QgsVectorFileWriter::writeAsVectorFormat( QgsVe
     // Shapefiles might contain multi types although wkbType() only reports singles
     if ( layer->storageType() == "ESRI Shapefile" )
     {
-      wkbType = QGis::multiType( wkbType );
+      const QgsFeatureIds &ids = layer->selectedFeaturesIds();
+      QgsFeatureIterator fit = layer->getFeatures();
+      QgsFeature fet;
+      while ( fit.nextFeature( fet ) )
+      {
+        if ( onlySelected && !ids.contains( fet.id() ) )
+          continue;
+
+        if ( fet.geometry() && fet.geometry()->wkbType() == QGis::multiType( wkbType ) )
+        {
+          wkbType = QGis::multiType( wkbType );
+          break;
+        }
+      }
     }
   }