Fix the test case converting abi11105.abw to EPUB file.
( the attachment at
  <https://bugzilla.abisource.com/show_bug.cgi?id=11105#c1> )

soffice.bin: .../sax/source/expatwrap/saxwriter.cxx:1184: virtual void
(anonymous namespace)::SAXWriter::endElement(const rtl::OUString &):
	Assertion `aName ==
	m_pSaxWriterHelper->m_DebugStartedElements.top()' failed.

We used to invoke handlePageSpan when starting a paragraph
or a table element that has master-page-name defined in the referred
style, and invoke closePageSpan when XMLBodyContentContext.

Limit the handling of page span to top-level paragraph or tables
so that it doesn't messed up in the nested ( paragraph that changed
it's page style in a table cell ) case.

Change-Id: Ic8637663aaa7506ced9758bd7ccd7233309e8557
Reviewed-on: https://gerrit.libreoffice.org/73214
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>