string.c: use `mrb_as_int` macro.
MODIFY
src/string.c
src/string.c
@@ -2844,7 +2844,7 @@ mrb_str_byteslice(mrb_state *mrb, mrb_value str)
}
}
else {
- beg = mrb_integer(mrb_to_integer(mrb, a1));
+ beg = mrb_as_int(mrb, a1);
len = 1;
empty = FALSE;
}

string.c: use `mrb_as_int` macro.