Avoid using `mrb_str_to_cstr` if possible

Because it always allocate new string. Replace with the followings:

- Use `RSRING_PTR` if string is guaranteed to be null-terminated.
- Use `mrb_string_value_cstr` or `mrb_get_args("z")` if return value isn't
  modified.

1 files changed, 1 insertions, 1 deletions

diff --git a/mrbgems/mruby-io/src/file_test.c b/mrbgems/mruby-io/src/file_test.c
index e429b06b3..7d36f79b3 100644
--- a/mrbgems/mruby-io/src/file_test.c
+++ b/mrbgems/mruby-io/src/file_test.c
@@ -63,7 +63,7 @@ mrb_stat0(mrb_state *mrb, mrb_value obj, struct stat *st, int do_lstat)
 
   tmp = mrb_funcall(mrb, obj, "is_a?", 1, str_klass);
   if (mrb_test(tmp)) {
-    char *path = mrb_locale_from_utf8(mrb_str_to_cstr(mrb, obj), -1);
+    char *path = mrb_locale_from_utf8(mrb_string_value_cstr(mrb, &obj), -1);
     int ret;
     if (do_lstat) {
       ret = LSTAT(path, st);