sendfile: code shrink

sendfile: code shrink

function                                             old     new   delta
printstr_base64                                        -      22     +22
printbuf_base64                                        -      11     +11
printfile_base64                                       -       9      +9
makemime_main                                        305     294     -11
encode_n_base64                                      236     223     -13
sendmail_main                                       1380    1366     -14
encode_base64                                         36       -     -36
------------------------------------------------------------------------------
(add/remove: 3/1 grow/shrink: 0/3 up/down: 42/-74)            Total: -32 bytes

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