So here we use `DECOMPOSITION_SIZE` to tell ICU how much buffer it has to play with (we'd previously already allocated this much space up above). Instead, I'd like to check the value of `status` to see if it's set to `U_BUFFER_OVERFLOW_ERROR`. If so, `uchar_txt_len` will be set to the actual length of the buffer we need (well, the length of `UChar`'s we need, so our allocated buffer needs to be `(sizeof(UChar)*uchar_txt_len)`.

Would love some help here /cc @scottjg @vmg