tdf#132321 tdf#133957 sw: for at-para fly, ignore anchor SwIndex

... because it's always 0, and not registered at the node; this fixes
the case when it's anchored at a non-empty last node of a section.

(follow-up to a0d0665060b75c1e7f0234b698c940d2f9d600f8)

Change-Id: I627e11e84a2dcfc2944d3c9f3fd22e3c3785e505
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/96350
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@cib.de>
(cherry picked from commit b314735568c1e9ab8ca52413017425bc2ef12973)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/96340
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
diff --git a/sw/source/core/undo/undobj.cxx b/sw/source/core/undo/undobj.cxx
index 3a3546c..0075dd3 100644
--- a/sw/source/core/undo/undobj.cxx
+++ b/sw/source/core/undo/undobj.cxx
@@ -1523,7 +1523,9 @@
    SwContentNode *const pNode(SwNodes::GoPrevious(&node));
    assert(pNode);
    assert(rAnchorPos.nNode <= node); // last valid anchor pos is last content
    return node == rAnchorPos.nNode && rAnchorPos.nContent == pNode->Len();
    return node == rAnchorPos.nNode
        // at-para fly has no SwIndex!
        && (rAnchorPos.nContent == pNode->Len() || rAnchorPos.nContent.GetIdxReg() == nullptr);
}

static bool IsAtStartOfSection(SwPosition const& rAnchorPos)