What happened is:

- the paragraph was split into two lines, at the correct position

- but then the first line checked how wide the tab portion can be, and
  there it concluded that it has a lot of space, so the tab portion was
  1418 twips wide, instead of the expected "almost zero" 69

The root of the problem was that first the text break was determined
using the TabOverMargin rules (more horizontal space), but later a check
validated the result ignoring the TabOverMargin flag (less horizontal
space). Fix this inconsistency by using GetLineWidth() in
SwTextPortion::Format_() instead of manual calculation.

Change-Id: Iaa7144341dfeaa8d177716dd87165598f11fd573
Reviewed-on: https://gerrit.libreoffice.org/61403Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins