Add missing QT_{BEGIN|END}_NAMESPACE

Change-Id: I9312c49f54cd231dd1129e1dbbed93aa959f67f0
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>

src/layouts/qquickgridlayoutengine.cpp

@@ -43,6 +43,7 @@
 #include "qquickgridlayoutengine_p.h"
 #include "qquicklayout_p.h"
 
+QT_BEGIN_NAMESPACE
 
 /*
   The layout engine assumes:
@@ -242,3 +243,4 @@ QLayoutPolicy::Policy QQuickGridLayoutItem::effectiveSizePolicy_helper(QQuickIte
     return fillExtent ? QLayoutPolicy::Preferred : QLayoutPolicy::Fixed;
 
 }
+QT_END_NAMESPACE