tdf#90808: sw: fix detection of duplicate CrossRefBookmarks

The check for existing bookmark positions is using the wrong position.
It must use the Start of the pam, because the constructor of
CrossRefBookmark only uses the Start of the pam.

Change-Id: I343f1c0e3571847a965a27571f01136810e83485

sw/source/core/doc/docbm.cxx

@@ -376,7 +376,7 @@ namespace sw { namespace mark
             " - more than USHRT_MAX marks are not supported correctly");
         // There should only be one CrossRefBookmark per Textnode per Type
         if ((eType == MarkType::CROSSREF_NUMITEM_BOOKMARK || eType == MarkType::CROSSREF_HEADING_BOOKMARK)
-            && (lcl_FindMarkAtPos(m_vBookmarks, *rPaM.GetPoint(), eType) != m_vBookmarks.end()))
+            && (lcl_FindMarkAtPos(m_vBookmarks, *rPaM.Start(), eType) != m_vBookmarks.end()))
         {   // this can happen via UNO API
             SAL_WARN("sw.core", "MarkManager::makeMark(..)"
                 " - refusing to create duplicate CrossRefBookmark");