Fix composer legend "Filter by Atlas Feature" does not save

Fix #16663

Author: nyalldawson

src/app/composer/qgscomposerlegendwidget.cpp

@@ -155,6 +155,7 @@ void QgsComposerLegendWidget::setGuiElements()
   mCheckBoxAutoUpdate->setChecked( mLegend->autoUpdateModel() );
 
   mCheckboxResizeContents->setChecked( mLegend->resizeToContents() );
+  mFilterLegendByAtlasCheckBox->setChecked( mLegend->legendFilterOutAtlas() );
 
   const QgsComposerMap* map = mLegend->composerMap();
   mMapComboBox->setItem( map );
@@ -922,6 +923,7 @@ void QgsComposerLegendWidget::blockAllSignals( bool b )
   mWmsLegendHeightSpinBox->blockSignals( b );
   mCheckboxResizeContents->blockSignals( b );
   mTitleSpaceBottomSpinBox->blockSignals( b );
+  mFilterLegendByAtlasCheckBox->blockSignals( b );
 }
 
 void QgsComposerLegendWidget::selectedChanged( const QModelIndex & current, const QModelIndex & previous )

src/core/composer/qgscomposerlegend.cpp

@@ -413,6 +413,8 @@ bool QgsComposerLegend::writeXML( QDomElement& elem, QDomDocument & doc ) const
     composerLegendElem.setAttribute( "legendFilterByMap", "1" );
   }
 
+  composerLegendElem.setAttribute( "legendFilterByAtlas", mFilterOutAtlas ? "1" : "0" );
+
   return _writeXML( composerLegendElem, doc );
 }
 
@@ -522,6 +524,7 @@ bool QgsComposerLegend::readXML( const QDomElement& itemElem, const QDomDocument
   {
     setComposerMap( mComposition->getComposerMapById( itemElem.attribute( "map" ).toInt() ) );
   }
+  mFilterOutAtlas = itemElem.attribute( "legendFilterByAtlas", "0" ).toInt();
 
   QDomElement oldLegendModelElem = itemElem.firstChildElement( "Model" );
   if ( !oldLegendModelElem.isNull() )