Fix hang when project with large number of layers has joins to same layers

Fixes qgis#55026

Author: nyalldawson

src/core/vector/qgsvectorlayerfeatureiterator.cpp

@@ -1231,6 +1231,7 @@ void QgsVectorLayerFeatureIterator::FetchJoinInfo::addJoinedAttributesDirect( Qg
   request.setSubsetOfAttributes( joinedAttributeIndices );
   request.setFilterExpression( subsetString );
   request.setLimit( 1 );
+  request.setRequestMayBeNested( true );
   QgsFeatureIterator fi = joinSource->getFeatures( request );
 
   // get first feature