GLX_NONE is not 0, so it doesn't work as end-of-list marker
The documentation explicitly mentions to use None or NULL
Fixes valgrind warning
==22686== Conditional jump or move depends on uninitialised value(s)
==22686== at 0x78949AF: glXCreatePbuffer (glx_pbuffer.c:709)
==22686== by 0xDD7F0E1: QGLXPbuffer::QGLXPbuffer(QOffscreenSurface*) (qglxintegration.cpp:515)
==22686== by 0xDD624B0: QXcbIntegration::createPlatformOffscreenSurface(QOffscreenSurface*) const (qxcbintegration.cpp:259)
==22686== by 0x4F1D6A2: QOffscreenSurface::create() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.2.1)
==22686== by 0xDD80248: QGLXContext::queryDummyContext() (qglxintegration.cpp:454)
==22686== by 0xDD803F0: QGLXContext::supportsThreading() (qglxintegration.cpp:488)
==22686== by 0x5BD9927: QSGRenderLoop::instance() (in /usr/lib/x86_64-linux-gnu/libQt5Quick.so.5.2.1)
==22686== by 0x5BF969E: QQuickWindowPrivate::init(QQuickWindow*) (in /usr/lib/x86_64-linux-gnu/libQt5Quick.so.5.2.1)
==22686== by 0x5C97BFC: QQuickView::QQuickView(QWindow*) (in /usr/lib/x86_64-linux-gnu/libQt5Quick.so.5.2.1)
==22686== by 0x40636F: startShell(int, char const**, void*) (main.cpp:91)
==22686== by 0x407125: main (main.cpp:193)
Change-Id: Ib4f5ae50f7e31d3fbeb5acf67753e1d8b9e434b0
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
af113cfc0f