glx: Prepare the DRI backends for GLX_EXT_no_config_context

This should be safe as these backends already support the EGL version of
this extension. DRI1 is not affected because it does not support
GLX_ARB_create_context anyway. DRI-Windows is not prepared to implement
this as there's no equivalent WGL extension, and wglCreateContextAttribs
seems to really want the HDC's pixel format to be set.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
diff --git a/src/glx/dri2_glx.c b/src/glx/dri2_glx.c
index e67a15f..0f44635 100644
--- a/src/glx/dri2_glx.c
+++ b/src/glx/dri2_glx.c
@@ -278,7 +278,7 @@
       goto error_exit;
    }
 
-   if (!glx_context_init(&pcp->base, &psc->base, &config->base))
+   if (!glx_context_init(&pcp->base, &psc->base, config_base))
       goto error_exit;
 
    ctx_attribs[num_ctx_attribs++] = __DRI_CTX_ATTRIB_MAJOR_VERSION;
@@ -317,7 +317,7 @@
    pcp->driContext =
       (*psc->dri2->createContextAttribs) (psc->driScreen,
 					  api,
-					  config->driConfig,
+					  config ? config->driConfig : NULL,
 					  shared,
 					  num_ctx_attribs / 2,
 					  ctx_attribs,
diff --git a/src/glx/dri3_glx.c b/src/glx/dri3_glx.c
index d613073..fa048f9 100644
--- a/src/glx/dri3_glx.c
+++ b/src/glx/dri3_glx.c
@@ -263,7 +263,7 @@
       goto error_exit;
    }
 
-   if (!glx_context_init(&pcp->base, &psc->base, &config->base))
+   if (!glx_context_init(&pcp->base, &psc->base, config_base))
       goto error_exit;
 
    ctx_attribs[num_ctx_attribs++] = __DRI_CTX_ATTRIB_MAJOR_VERSION;
@@ -297,7 +297,8 @@
    pcp->driContext =
       (*psc->image_driver->createContextAttribs) (psc->driScreen,
                                                   api,
-                                                  config->driConfig,
+                                                  config ? config->driConfig
+                                                         : NULL,
                                                   shared,
                                                   num_ctx_attribs / 2,
                                                   ctx_attribs,
diff --git a/src/glx/drisw_glx.c b/src/glx/drisw_glx.c
index a471856..2f0675a 100644
--- a/src/glx/drisw_glx.c
+++ b/src/glx/drisw_glx.c
@@ -455,7 +455,7 @@
    if (pcp == NULL)
       return NULL;
 
-   if (!glx_context_init(&pcp->base, &psc->base, &config->base)) {
+   if (!glx_context_init(&pcp->base, &psc->base, config_base)) {
       free(pcp);
       return NULL;
    }
@@ -483,7 +483,7 @@
    pcp->driContext =
       (*psc->swrast->createContextAttribs) (psc->driScreen,
 					    api,
-					    config->driConfig,
+					    config ? config->driConfig : 0,
 					    shared,
 					    num_ctx_attribs / 2,
 					    ctx_attribs,