Make sure relations are reloaded when setting edit config

Author: m-kuhn

src/core/qgsvectorlayer.cpp

@@ -3810,6 +3810,7 @@ void QgsVectorLayer::setEditFormConfig( const QgsEditFormConfig &editFormConfig
     return;
 
   mEditFormConfig = editFormConfig;
+  mEditFormConfig.onRelationsLoaded();
   emit editFormConfigChanged();
 }