mhshow/test-charset: printf(1)'s octal doesn't need a leading zero.

mhshow/test-charset: printf(1)'s octal doesn't need a leading zero.

The `\0344' was being interpreted as `\034' and `4'.  This can still be
converted from EBCDIC-US to UTF-8 by iconv(1) so the test worked, but it
was misleading.  Remove the leading zero as printf's octal escape is
`\nnn' where nnn is one to three octal digits.  It's echo(1) that
insists on a leading zero.  Fixes 6fd1d18f.