if no new cell exists, create hidden broadcaster cell, fdo#51368

Change-Id: I61b96a0e164269ef85778cba7865d6488ebac79d

sc/source/core/data/column3.cxx

@@ -1395,6 +1395,9 @@ bool ScColumn::SetString( SCROW nRow, SCTAB nTabP, const String& rString,
             SvtBroadcaster* pBC = pOldCell->ReleaseBroadcaster();
             if (pNewCell || pBC)
             {
+                if(!pNewCell)
+                    pNewCell = new ScNoteCell();
+
                 if (pBC)
                 {
                     pNewCell->TakeBroadcaster(pBC);