The topmost shape may not have 0 depth, but something larger.

In that case at least it's safe to still use fill & line properties. The
B1 quadrant of the test file now has the proper orange background, and
B2's border is also properly orange.

Change-Id: Iccc5f6993693a0f1cf8f50d163003c24d3ad690e
Reviewed-on: https://gerrit.libreoffice.org/68104Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins