fix crash on opening symbol levels dialog when using categorized renderer with showClassifiers

Author: jef-n

src/gui/symbology-ng/qgssymbollevelsv2dialog.cpp

@@ -73,12 +73,18 @@ QgsSymbolLevelsV2Dialog::QgsSymbolLevelsV2Dialog( QgsLegendSymbolList list, bool
 
   connect( chkEnable, SIGNAL( clicked() ), this, SLOT( updateUi() ) );
 
+  if ( mList.count() > 0 && !mList[0].second )
+  {
+    // remove symbolless entry (probably classifier of categorized renderer)
+    mList.removeFirst();
+  }
+
   int maxLayers = 0;
-  tableLevels->setRowCount( list.count() );
-  for ( int i = 0; i < list.count(); i++ )
+  tableLevels->setRowCount( mList.count() );
+  for ( int i = 0; i < mList.count(); i++ )
   {
-    QgsSymbolV2* sym = list[i].second;
-    QString label = list[i].first;
+    QgsSymbolV2* sym = mList[i].second;
+    QString label = mList[i].first;
 
     // set icons for the rows
     QIcon icon = QgsSymbolLayerV2Utils::symbolPreviewIcon( sym, QSize( 16, 16 ) );