fdo#74790: sw: Compare Document: fix assertions about RSID-only hints

For ordinary documents the SwTxtNode::MakeFrm() would set the
m_bFormatIgnoreStart/End flags of the RSID-only hints, but the document
loaded by Compare Document (and Merge Document) is special because it
is loaded, there are editing operations on it, but it has no layout,
so the assertions about these flags trigger.

(regression from 6db39dbd7378351f6476f6db25eb7110c9cfb291)

Change-Id: I8a6e02b68f22e609640adbe93ff194e4081d9856
(cherry picked from commit 80b131038d2375c9855ee5fbe225e75bdad2645e)
Reviewed-on: https://gerrit.libreoffice.org/9274
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>