sw: fix STL asserts in lcl_MoveAllLowerObjs *again*

Comment added in cf91483690291272f48ff95c1aebd165da8ae4f0 evidently
insufficient.

(regression from b415494bf0468b74318b61f114e2ff4ae68c00ee)

Change-Id: I9a017aefc3a77b0760fcdc3b8e43ff7c6ac516ac
diff --git a/sw/source/core/layout/pagechg.cxx b/sw/source/core/layout/pagechg.cxx
index c722da9..7ea39752 100644
--- a/sw/source/core/layout/pagechg.cxx
+++ b/sw/source/core/layout/pagechg.cxx
@@ -1763,8 +1763,10 @@ static void lcl_MoveAllLowerObjs( SwFrame* pFrame, const Point& rOffset )

    // note: pSortedObj elements may be removed and inserted from
    // MoveObjectIfActive(), invalidating iterators
    for (SwAnchoredObject* pAnchoredObj : *pSortedObj)
    // DO NOT CONVERT THIS TO A C++11 FOR LOOP, IT DID NOT WORK THE LAST 2 TIMES
    for (size_t i = 0; i < pSortedObj->size(); ++i)
    {
        SwAnchoredObject *const pAnchoredObj = (*pSortedObj)[i];
        const SwFrameFormat& rObjFormat = pAnchoredObj->GetFrameFormat();
        const SwFormatAnchor& rAnchor = rObjFormat.GetAnchor();