Check if there is an old item before removing it

Check if there is an old item before removing it

If something had changed with the menu item before it had actually been
originally added to the native menu then this would crash when trying
to remove a null item from the native menu.  This prevents that from
happening.

Change-Id: I8d78b5504759225364d5fd051a23c8d6dbd7d1eb
Reviewed-by: James Turner <james.turner@kdab.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>