Fix: missing null byte delimeter in PrivateFrame

[0xNF]

The spec for PrivateFrames says that a null byte should be inserted after the owner_identifier field.

Currently, if one adds a private frame, they will encounter read failures when decoding tags.

This PR adds the null byte to the encoder which lets tags with PrivateFrames be decoded properly.

[polyfloyd]

Cool, thanks for fixing. Please make the CI happy and I'll merge this :)

[0xNF]

I don't know what to do about that style failure.

When I run cargo clippy --all-features -- -Dwarnings on my local device, my output doesn't reflect the same failure:

  Downloaded tokio-macros v2.3.0
  Downloaded quote v1.0.36
  Downloaded bytes v1.6.0
  Downloaded pin-project-lite v0.2.14
  Downloaded proc-macro2 v1.0.86
  Downloaded syn v2.0.68
  Downloaded tokio v1.38.0
  Downloaded 7 crates (1.2 MB) in 0.69s
   Compiling proc-macro2 v1.0.86
   Compiling unicode-ident v1.0.12
    Checking bytes v1.6.0
    Checking pin-project-lite v0.2.14
   Compiling quote v1.0.36
   Compiling syn v2.0.68
   Compiling tokio-macros v2.3.0
    Checking tokio v1.38.0
    Checking id3 v1.13.1 (/mnt/c/Users/0xnf/projects/experiments/rust-id3)
    Finished dev [unoptimized + debuginfo] target(s) in 15.25s

But more than that, I also think it's not correct? The Storage.reader function is implemented by StorageFile, which in turn is called by a bunch of test functions, like plain_write_to_padding and plain_writer_shrink.

This PR doesn't touch the storage objects at all, so I don't want to make a bigger change than necessary. What do you recommend?

[polyfloyd]

Oh hmm yeah, I checked locally and that does not seem related. I'll fix it when I have some time :)