Conditional formatting on relation reference widget

in case we have additional display expressions there does use the conditional formatting for the row
and in case there is only one fieldname used in the display expression it does use this as well

Fix: #18521

src/core/qgsfeaturefiltermodel.cpp

@@ -448,28 +448,23 @@ QgsConditionalStyle QgsFeatureFilterModel::featureStyle( const QgsFeature &featu
   QgsVectorLayer *layer = mSourceLayer;
   QgsFeatureId fid = feature.id();
   mExpressionContext.setFeature( feature );
-  QgsConditionalStyle style;
-
-  if ( mEntryStylesMap.contains( fid ) )
-  {
-    style = mEntryStylesMap.value( fid );
-  }
 
   auto styles = QgsConditionalStyle::matchingConditionalStyles( layer->conditionalStyles()->rowStyles(), QVariant(),  mExpressionContext );
 
-  if ( mDisplayExpression.isField() )
+  if ( mDisplayExpression.referencedColumns().count() == 1 )
   {
     // Style specific for this field
     QString fieldName = *mDisplayExpression.referencedColumns().constBegin();
     const auto allStyles = layer->conditionalStyles()->fieldStyles( fieldName );
     const auto matchingFieldStyles = QgsConditionalStyle::matchingConditionalStyles( allStyles, feature.attribute( fieldName ),  mExpressionContext );
 
     styles += matchingFieldStyles;
-
-    style = QgsConditionalStyle::compressStyles( styles );
-    mEntryStylesMap.insert( fid, style );
   }
 
+  QgsConditionalStyle style;
+  style = QgsConditionalStyle::compressStyles( styles );
+  mEntryStylesMap.insert( fid, style );
+
   return style;
 }