st/mesa: init winsys buffers list only if context creation succeeds

Fixes piglit test crash when context creation fails.

v2: As suggested by Brian, move the init to st_create_context_priv()

Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/state_tracker/st_context.c

@@ -476,6 +476,9 @@ st_create_context_priv( struct gl_context *ctx, struct pipe_context *pipe,
    _mesa_initialize_vbo_vtxfmt(ctx);
    st_init_driver_flags(st);
 
+   /* Initialize context's winsys buffers list */
+   LIST_INITHEAD(&st->winsys_buffers);
+
    return st;
 }
 
@@ -576,9 +579,6 @@ struct st_context *st_create_context(gl_api api, struct pipe_context *pipe,
       _mesa_destroy_context(ctx);
    }
 
-   /* Initialize context's winsys buffers list */
-   LIST_INITHEAD(&st->winsys_buffers);
-
    return st;
 }