print: avoid last few allocs when writing bytes
print: avoid last few allocs when writing bytes

name      old time/op    new time/op    delta
Fprint-4    12.0µs ± 1%    12.5µs ± 1%   +4.42%  (p=0.008 n=5+5)

name      old alloc/op   new alloc/op   delta
Fprint-4      360B ± 0%      320B ± 0%  -11.11%  (p=0.002 n=6+6)

name      old allocs/op  new allocs/op  delta
Fprint-4      56.0 ± 0%       8.0 ± 0%  -85.71%  (p=0.002 n=6+6)

mvdan/sh,mvdan/sh,mvdan/sh,mvdan/sh