FTA: 修改以避开 utf8/Unicode 字符串长度计算中的错误

For posterity sake, I want to document these bugs -- though the library is clearly not being maintained! -- so maybe it saves others debugging time. But rather than posting a PR to fix these, since it almost certainly won't be accepted, I'm going to do something different later in this message: provide a "hack" (a run-time patch of the instance!) that not only gets around all these utf8/unicode bugs, but also provides something feature-wise this library arguably always should have had: a way to encode arbitrary binary data into the QR without needing to go through JS strings (utf16).