Have __glImageSize handle format GL_DEPTH_STENCIL_NV the same way as the server does
Have __glImageSize handle format GL_DEPTH_STENCIL_NV the same way as the server does

There is a mismatch between the way the X server and GLX library
calculates the image size for format GL_DEPTH_STENCIL(|_NV|_EXT)

See https://bugs.freedesktop.org/show_bug.cgi?id=30102

Signed-off-by: Jon TURNEY <45846cba2ea093796a8b1c25d70d679d8107179f@dronecode.org.uk>

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