util/vbuf: fix index_bo leak

When indices are unrolled we still have to release the index_bo
references passed to us.

Cc: mesa-stable
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/8272
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22237>

src/gallium/auxiliary/util/u_vbuf.c

@@ -1729,6 +1729,8 @@ void u_vbuf_draw_vbo(struct pipe_context *pipe, const struct pipe_draw_info *inf
          }
 
          if (unroll_indices) {
+            if (!new_info.has_user_indices && info->take_index_buffer_ownership)
+               pipe_drop_resource_references(new_info.index.resource, 1);
             new_info.index_size = 0;
             new_draw.index_bias = 0;
             new_info.index_bounds_valid = true;