sed: a communal variable managed to slip past 'size'

sed: a communal variable managed to slip past 'size'
('size' happily displays 0 bytes in data and bss,
but in reality sed.o used 180 bytes of it). Oh well.
function                                             old     new   delta
pipe_putc                                             67      76      +9
sed_main                                             627     633      +6
get_next_line                                        161     166      +5
bbg                                                  180       -    -180
(add/remove: 0/1 grow/shrink: 3/0 up/down: 20/-180)          Total: -160 bytes

sed: also make sed -i failure message less cryptic