highlight on initialization

(cherry-picked from 9ff71a0)

src/gui/editorwidgets/qgsrelationreferencewidget.cpp

@@ -555,7 +555,9 @@ void QgsRelationReferenceWidget::init()
 
     // Only connect after iterating, to have only one iterator on the referenced table at once
     connect( mComboBox, static_cast<void ( QComboBox::* )( int )>( &QComboBox::currentIndexChanged ), this, &QgsRelationReferenceWidget::comboReferenceChanged );
+
     mReferencedLayer->getFeatures( mComboBox->currentFeatureRequest() ).nextFeature( mFeature );
+    highlightFeature( mFeature );
     updateAttributeEditorFrame( mFeature );
     QApplication::restoreOverrideCursor();
   }