SfxDispatcher::Execute(sal_uInt16 nSlot, SfxCallMode eCall,
    const SfxPoolItem*  pArg1, ...)
assigns the varargs to a "const SfxPoolItem *", so passing in
"0L" is only correct if long is 64-bit, but on WNT 64-bit long is
32-bit, so use "nullptr" already.

Change-Id: Iaf41efa795fd4439daab7ed7ec334d8ad8c476f3