The parsing in parse_set and parse_unset saves, overwrites with a NUL, and restores a character in the string that is being parsed. If there is a malloc failure between overwriting and restoring, the restore is not done. This commit changes that behaviour to restore before returning.
straconcat reads the args with va_arg(ap, const unsigned char *),
and the NULL macro may have the wrong type (e.g. int).
Many places pass string literals of type char * to straconcat. This
is in principle also a violation, but I'm ignoring it for now because
if it becomes a problem with some C implementation, then so will the
use of unsigned char * with printf "%s", which is so widespread in
ELinks that I'm not going to try fixing it now.
