Add missing emission of activated(QString)

This signal got missed when 3fb0d851a was submitted so this compliments
that fix.

Change-Id: I91d20b709fce2c78d41166779954a3bb618feb37
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@theqtcompany.com>

src/widgets/widgets/qcombobox.cpp

@@ -2429,6 +2429,7 @@ struct IndexSetter {
     {
         cb->setCurrentIndex(index);
         emit cb->activated(index);
+        emit cb->activated(cb->itemText(index));
     }
 };
 }