sw: fix ~SwIndexReg() assertion on import of tdf92157-1.docx

Problem is that the TextBox SwFrmFmt of a draw object gets a FLY_AS_CHAR
anchor set, which is then not updated later before nodes are deleted.

(regression from c7307c77)

(cherry picked from commit 9dbb88fc)

Change-Id: I906ee47b5c30944a08fd8a0d7d6ea8b8c9e6a6a8
Reviewed-on: https://gerrit.libreoffice.org/17580Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

sw/source/core/doc/DocumentLayoutManager.cxx

@@ -496,7 +496,14 @@ SwFrameFormat *DocumentLayoutManager::CopyLayoutFormat(
     // If the draw format has a TextBox, then copy its fly format as well.
     if (SwFrameFormat* pSourceTextBox = SwTextBoxHelper::findTextBox(&rSource))
     {
-        SwFrameFormat* pDestTextBox = CopyLayoutFormat(*pSourceTextBox, rNewAnchor, bSetTextFlyAtt, bMakeFrms);
+        SwFormatAnchor boxAnchor(rNewAnchor);
+        if (FLY_AS_CHAR == boxAnchor.GetAnchorId())
+        {
+            // AS_CHAR *must not* be set on textbox fly-frame
+            boxAnchor.SetType(FLY_AT_CHAR);
+        }
+        SwFrameFormat* pDestTextBox = CopyLayoutFormat(*pSourceTextBox,
+                boxAnchor, bSetTextFlyAtt, bMakeFrms);
         SwAttrSet aSet(pDest->GetAttrSet());
         SwFormatContent aContent(pDestTextBox->GetContent().GetContentIdx()->GetNode().GetStartNode());
         aSet.Put(aContent);