fdo#74357 DOCX import: avoid layout problem with automatic spacing

Commit 279ff2e03371542d014bf281e73282ba8080cf6b (bnc#816593 DOCX import:
fix auto para spacing without compat option, 2013-08-28) corrected the
value of "auto" paragraph spacing, but unfortunately this triggers a
layout problem:

warn:legacy.osl:12692:1:sw/source/core/layout/tabfrm.cxx:2513: debug assertion: <SwTabFrm::MakeAll()> - format of table lowers suppressed by fix i44910

resulting in "the rest of the table is not rendered by the layout".

Given that we backported the original fix to stable branches as well,
just stay on the safe side and revert back to the original behavior in
case the document requests the web layout.

Change-Id: I72683530b5218beff084bec8218cc99946b44802