Fix a <= 5-byte buffer overwrite in print_bin()

Fix a <= 5-byte buffer overwrite in print_bin()

If the offset is > 124, this function would overwrite between 1 and 5 bytes
of stack space after str[128]. So for a quick fix extend the buffer by 5
bytes. Obviously this is the permanent fix chosen elswehere. The proper fix
will be to rewrite this function from scratch.

Reported in detail by Masaru Masuda, many thanks!
Fixes https://github.com/libressl/openbsd/issues/145

begrudging ok from beck