string.c (mrb_str_index_m): no need to align the position; ref
MODIFY
src/string.c
src/string.c
@@ -1772,7 +1772,6 @@ mrb_str_index_m(mrb_state *mrb, mrb_value str)
pos = str_index_str_by_char(mrb, str, sub, pos);
if (pos == -1) return mrb_nil_value();
- BYTES_ALIGN_CHECK(pos);
return mrb_int_value(mrb, pos);
}

string.c (mrb_str_index_m): no need to align the position; ref #4569