The old code only worked when left and first margin was 0; feed the
relevant margin to SwTextFormatInfo, so SwTextFormatInfo::GetLineWidth()
can compare against the right rectangle.

This way TabOverMargin compat flag results in layout that matches the
Word behavior for all 3 bugdocs from the bugreport.

Change-Id: I6f81ad33b14e95ba4213c8956b3a9790ba6eee84
Reviewed-on: https://gerrit.libreoffice.org/61518Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins