extend_buffers
err = extend_buffers (mctx, next_char_idx + 1);
err = extend_buffers (mctx, next_state_log_idx + 1);
static reg_errcode_t extend_buffers (re_match_context_t *mctx, int min_len);
err = extend_buffers (mctx, bkref_str_off + 1);