erase the correct element in ScColumn::Delete(), not the last one

This fixes the dreaded crash in sc_unoapi test.
Thanks to Kohei for pointing in the right direction.

sc/source/core/data/column3.cxx

@@ -172,7 +172,7 @@ void ScColumn::Delete( SCROW nRow )
         else
         {
             pNoteCell->Delete();
-            maItems.erase(maItems.end() - 1);
+            maItems.erase( maItems.begin() + nIndex);
             //  Soll man hier den Speicher freigeben (delta)? Wird dann langsamer!
         }
         pCell->EndListeningTo( pDocument );