bc: do not allocate line editing state until needed

function                                             old     new   delta
xc_read_line                                         324     353     +29
free_line_input_t                                     34      39      +5
xc_vm_init                                           656     640     -16
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 34/-16)             Total: 18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
5 files changed