Fix incorrect calculation of priority for diagrams (fix #4692)

Author: nyalldawson

src/core/qgspallabeling.cpp

@@ -3382,7 +3382,8 @@ int QgsPalLabeling::prepareLayer( QgsVectorLayer* layer, QStringList& attrNames,
 
 int QgsPalLabeling::addDiagramLayer( QgsVectorLayer* layer, const QgsDiagramLayerSettings *s )
 {
-  Layer* l = mPal->addLayer( layer->id().append( "d" ).toUtf8().data(), -1, -1, pal::Arrangement( s->placement ), METER, s->priority, s->obstacle, true, true );
+  double priority = 1 - s->priority / 10.0; // convert 0..10 --> 1..0
+  Layer* l = mPal->addLayer( layer->id().append( "d" ).toUtf8().data(), -1, -1, pal::Arrangement( s->placement ), METER, priority, s->obstacle, true, true );
   l->setArrangementFlags( s->placementFlags );
 
   mActiveDiagramLayers.insert( layer->id(), *s );