sw: layout: fix bad split table resulting in empty cell HEADmaster

The problem is that the table goes into an infinite loop of splitting
and joining, because there is a temporarily negative PrtArea height in
the top row's cells (-170), because of setting all heights to 0.

This causes an inconsistency where it is first joined because in
ShouldBwdMoved() another line of text in the right column cell can move
backward, but then there isn't enough space for another row as the
negative cell PrtArea height is added to the available space and so the
line won't fit in SwTextFrameBreak::IsInside(); the same situation
occurs until a "Looping Louie" aborts the iteration with a bad result.

This is somehow caused by the hidden section following the table, but
not sure how exactly (the "if (pNxt->IsHiddenNow()) bCalcNxt = false"
suspect code was actually added in a later commit).

Prevent it by preventing negative PrtArea heights.

(regression from commit 0c96119895b347f8eb5bb89f393351bd3c02b9f1)

Change-Id: I36ce8a8bf750cf407cece5ad3cc23374182179de
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/180719
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@allotropia.de>

0 files changed, 0 insertions, 0 deletions