Embedded documents had "Untitled" name.
This patch shows "<root document> (Embedded document)"
string in the title bar.

Change-Id: I6283240415f9e0c07c4c69672732a7c14eea9f5d
Reviewed-on: https://gerrit.libreoffice.org/39835Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>