draw: fix missing line viewport transformation

Fixes: 00627b4f ("aux/draw: add guardband clipping for lines")

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Roland Scheidegger <roland.scheidegger@broadcom.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36653>

src/gallium/auxiliary/draw/draw_cliptest_tmp.h

@@ -159,6 +159,14 @@ TAG(do_cliptest)(struct pt_post_vs *pvs,
          need_pipeline |= out->clipmask;
       }
 
+      /* For the window transformation, the first 4 (xy) clip planes should
+       * normally be handled by guardband clipping in clip_line_guard_xy, but
+       * it hasn't been fully implemented yet, so we'll have to do it here.
+       * Otherwise we'd skip it for being redundant.
+       */
+      if (flags & DO_CLIP_XY_GUARD_BAND)
+         mask &= 0xfffffff0;
+
       /*
        * Transform the vertex position from clip coords to window coords,
        * if the vertex is unclipped.