Fix QtVersion::invalidReason for symbian/desktop/simulator

Actually pass on the base qt version value...
Also fix a small issue on the qt versions page that prevented the
invalid reason showing up for a nameless version

Task-Nr: QTCREATORBUG-4899

src/plugins/qt4projectmanager/qt-desktop/simulatorqtversion.cpp

@@ -84,7 +84,7 @@ QString SimulatorQtVersion::invalidReason() const
     QString tmp = BaseQtVersion::invalidReason();
     if (tmp.isEmpty() && qtAbis().isEmpty())
         return QCoreApplication::translate("QtVersion", "Failed to detect the ABI(s) used by the Qt version.");
-    return QString();
+    return tmp;
 }
 
 QList<ProjectExplorer::Abi> SimulatorQtVersion::qtAbis() const