Fixes value relation line edit not found values

When there is no match in the relation layer,
show "(no selection)" instead of NOT updating
the widget (which was the reported issue).

Fixes qgis#38552

(cherry picked from commit 448f7d9)

src/gui/editorwidgets/qgsvaluerelationwidgetwrapper.cpp

@@ -243,14 +243,22 @@ void QgsValueRelationWidgetWrapper::updateValues( const QVariant &value, const Q
   }
   else if ( mLineEdit )
   {
+    mLineEdit->clear();
+    bool wasFound { false };
     for ( const QgsValueRelationFieldFormatter::ValueRelationItem &i : qgis::as_const( mCache ) )
     {
       if ( i.key == value )
       {
         mLineEdit->setText( i.value );
+        wasFound = true;
         break;
       }
     }
+    // Value could not be found
+    if ( ! wasFound )
+    {
+      mLineEdit->setText( tr( "(no selection)" ) );
+    }
   }
 }