Deleting last message

[Stewart Evans <stewart lutris com>]

Deleting the last message in a mailbox causes no message to be selected.  A
more intuitive behavior seems to me to be that it select whatever is the
new last message.  Adding these two lines to the end of balsa_index_del
seemed to do the trick:

if (bi_get_largest_selected(GTK_CLIST (bindex) ) < 0 )
      balsa_index_select_next (bindex);

-- Stewart