Fix __glXInitializeVisualConfigFromTags's handling of unrecognized fbconfig tags.

Fix __glXInitializeVisualConfigFromTags's handling of unrecognized fbconfig tags.

__glXInitializeVisualConfigFromTags doesn't skip the payload of
unrecognized tags.  Instead, it treats the value as if it were the
next tag, which can happen if the server's GLX extension is not
Mesa's.  For example, this falls down when NVIDIA sends a
GLX_FLOAT_COMPONENTS_NV = 0 pair, causing
__glXInitializeVisualConfigFromTags to bail out early.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>