draw: Add a null check for draw.

There is an earlier null check for draw so draw could be null here as
well.

Fixes "Dereference after null check" defect reported by Coverity.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/gallium/auxiliary/draw/draw_pipe_unfilled.c

@@ -237,7 +237,7 @@ draw_unfilled_prepare_outputs( struct draw_context *draw,
    boolean is_unfilled = (rast &&
                           (rast->fill_front != PIPE_POLYGON_MODE_FILL ||
                            rast->fill_back != PIPE_POLYGON_MODE_FILL));
-   const struct draw_fragment_shader *fs = draw->fs.fragment_shader;
+   const struct draw_fragment_shader *fs = draw ? draw->fs.fragment_shader : 0;
 
    if (is_unfilled && fs && fs->info.uses_frontface)  {
       unfilled->face_slot = draw_alloc_extra_vertex_attrib(