Part of code
   1299             ImplHeadItemList::iterator it = mpItemList->begin();
   1300             ::std::advance( it, nPos );
   1301             ImplHeadItem* pItem = *it;
   1302             mpItemList->erase( it );
   1303             if ( nNewPos < nPos ) <-- case move to left
   1304                 nPos = nNewPos;
   1305             it = mpItemList->begin();
   1306             ::std::advance( it, nPos );
   1307             mpItemList->insert( it, pItem );
So in move to right case, we erase and insert pItem at the same place
We just have to use nNewPos in all cases

regression from bd24a310

Also add back "ImplUpdate" call erroneously removed in merge
commit 67d2af6f
(there is an ImplUpdate call in each parent of that merge commit)

Change-Id: I100b0c6874b366f777c5d38470fcee7a9a7326df
Reviewed-on: https://gerrit.libreoffice.org/14777Reviewed-by: Lionel Elie Mamane <lionel@mamane.lu>
Tested-by: Lionel Elie Mamane <lionel@mamane.lu>