[waffle] Bad parameters passed to glXChooseFBConfig

[Brian Paul]

In glx_config.c we're passing -1 for GLX_DEPTH_SIZE and/or
GLX_STENCIL_SIZE when those buffers are not requested.  The negative
values seem to be the defaults in the wcore_config_attrs object,
coming from WAFFLE_DONT_CARE=-1.

Per the glXGetFBConfig() man page, negative values are not allowed for
those attributes.

Mesa's fake GLX code (used for xlib/swrast) isn't handling this
properly and a lot of piglit tests fail as a consequence.

One possible fix would be to add some zero-clamping code like this in
glx_config_choose():

        GLX_DEPTH_SIZE,         MAX2(0, attrs->depth_size),
        GLX_STENCIL_SIZE,       MAX2(0, attrs->stencil_size),

I suspect other GLX attribs are also getting illegal negative values too.

-Brian