st/mesa: add support for GL_ARB_texture_buffer_range

v2: Update to handle BufferSize being -1 and return a NULL sampler
view if the specified range would cause out of bounds access.

Reviewed-by: Brian Paul <brianp@vmware.com>
Acked-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/state_tracker/st_extensions.c

@@ -685,6 +685,13 @@ void st_init_extensions(struct st_context *st)
    }
    if (screen->get_param(screen, PIPE_CAP_TEXTURE_BUFFER_OBJECTS)) {
       ctx->Extensions.ARB_texture_buffer_object = GL_TRUE;
+
+      ctx->Const.TextureBufferOffsetAlignment =
+         screen->get_param(screen, PIPE_CAP_TEXTURE_BUFFER_OFFSET_ALIGNMENT);
+
+      if (ctx->Const.TextureBufferOffsetAlignment)
+         ctx->Extensions.ARB_texture_buffer_range = GL_TRUE;
+
       init_format_extensions(st, tbo_rgb32, Elements(tbo_rgb32),
                              PIPE_BUFFER, PIPE_BIND_SAMPLER_VIEW);
    }