Initialize member variable.

Change-Id: Ica42c77614fa4fa9ae7692e00d3fc796219aacdc
Reviewed-on: http://codereview.qt.nokia.com/466
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jørgen Lind <jorgen.lind@nokia.com>

src/gui/kernel/qplatformglcontext_qpa.cpp

@@ -62,7 +62,8 @@ class QPlatformGLContextPrivate
 {
 public:
     QPlatformGLContextPrivate()
-        :qGLContextHandle(0)
+        : qGLContextHandle(0)
+        , qGLContextDeleteFunction(0)
     {
     }