The visible effect of this was that the 2nd level text nodes were
missing from the layout result.

The cause is that when it comes to counting nodes of a condition, we
assumed that the current layout node is a presentation of a model node,
but this is not necessarily true.

Fix the problem doing a "first presentation child of", then a "presentation
of" navigation in that case, which leads us to the correct model node,
so counting its children works.

(An alternative way of getting non-zero children would be a
"presentation parent of" navigation, followed by a "presentation of"
navigation, but that would lead us to the document root, so we would
count the number of 1st level elements, not the correct 2nd level
elements.)

Change-Id: Iccebe0e2e56b7acb7fbe2c38a7c9ebb2abb309b9
Reviewed-on: https://gerrit.libreoffice.org/62703Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins