glx: Work around X servers reporting bogus values of GLX_SWAP_METHOD_OML

glx: Work around X servers reporting bogus values of GLX_SWAP_METHOD_OML

Due to the recently fixed bug where dri drivers didn't report a correct
__DRI_ATTRIB_SWAP_METHOD value, and the fact that X servers just forward this
incorrect value (from the AIGLX dri driver) untranslated as
GLX_SWAP_METHOD_OML, the latter value might be undefined when old dri AIGLX
drivers are used, which breaks client fbconfig matching with server fbconfigs.

So work around this by assuming GLX_SWAP_METHOD_UNDEFINED when a bogus value
is read.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>