[ruby/stringio] Fix ascii_only? flag in strio_write

(https://github.com/ruby/stringio/pull/77)

Followup of #79

`rb_str_resize()` was changed by https://github.com/ruby/ruby/commit/b0b9f7201acab05c2a3ad92c3043a1f01df3e17f  .

```c
rb_str_resize(string, shorter) // clear ENC_CODERANGE in some case
rb_str_resize(string, longer) // does not clear ENC_CODERANGE anymore
```

```c
// rb_str_resize in string.c
if (slen > len && ENC_CODERANGE(str) != ENC_CODERANGE_7BIT) {
  ENC_CODERANGE_CLEAR(str);
}
```

I think this change is based on an assumption that appending null bytes
will not change flag `ascii_only?`.

`strio_extend()` will make the string longer if needed, and update the
flags correctly for appending null bytes.
Before `memmove()`, we need to `rb_str_modify()` because updated flags are not
updated for `memmove()`.

https://github.com/ruby/stringio/commit/b31a538576

0 files changed, 0 insertions, 0 deletions