Fix call to representValue in identifydialog

This should fix the problem of queries with WHERE (id = 'NULL') when the
string 'NULL' cannot be converted to integer / uuid, as seen with
relation reference widgets.

(cherry-picked from 5e70e96)

Author: Hugo Mercier

src/app/qgsidentifyresultsdialog.cpp

@@ -584,7 +584,7 @@ void QgsIdentifyResultsDialog::addFeature( QgsVectorLayer *vlayer, const QgsFeat
       continue;
 
     QString value = fields.at( i ).displayString( attrs.at( i ) );
-    QString value2 = representValue( vlayer, fields.at( i ).name(), value );
+    QString value2 = representValue( vlayer, fields.at( i ).name(), attrs.at( i ) );
 
     tblResults->setRowCount( j + 1 );