Support for prefix garbage?

[Melirius]

As I can see, LEPTON_HEADER_PREFIX_GARBAGE_MARKER is defined, but is not used (self.write_lepton_jpeg_garbage_if_needed(&mut mrw, false)?; is always with false), and Lepton file encoded with -embedded=XXX will exit the library by return err_exit_code(ExitCode::BadLeptonFile, "unknown data found"); Even if not supporting prefix garbage in encode, we can support decoding such files without difficulties.