Fix LastMessage Selection.

    The id of the storagmodel is not constant over the lifecycle
    of a storagemodel. Immediatly after something new is selected
    in the selectionmodel the id's change to the new selection.
    This caused the messagelist manager to save the last selected
    message not for the colletions that were selected
    but for the collections about to be selected.
    Since the messageId then did not exist in the newly selected
    collection the messageId of the lastselected message was discarded.

    BUG: 272417