If a line happens to be invisible (e.g. in too thin cell of a table)
then aLine.FormatLine(nStart) returns nStart, and
aLine.Insert( new SwLineLayout() ) is executed until OOM.

Change-Id: I9b12cf2f1f3f1987cd8ce380b1d85196ffe95e5e
Reviewed-on: https://gerrit.libreoffice.org/15542Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>