maintainer's notes:
commit
a223dbd27ae36fe53f9f67f86caf685b729593fc added the reverse
conversions to JIS-based encodings, but omitted the check for remining
buffer space in the case where the next character to be written was
single-byte, allowing conversion to continue past the end of the
destination buffer.
if (*outb < 1) goto toobig;
if (c<256 && c==legacy_map(tomap, c)) {
revout:
+ if (*outb < 1) goto toobig;
*(*out)++ = c;
*outb -= 1;
break;