fix clippy::into_iter_on_array error in decoder

[scottmcm]

Rust is trying to add IntoIterator for arrays, which would break this. So might as well do it the way that's forward-compatible and also shorter.

[scottmcm]

CI failure doesn't look like the fault of this change:

failed to parse manifest at /home/travis/.cargo/registry/src/github.aaakk.us.kg-1ecc6299db9ec823/cfg-if-0.1.10/Cargo.toml
(All the other builds are fine)

[CryZe]

Looks like rayon isn't actually compatible with 1.28 anymore (due to some indirect dependency on the latest cfg-if).

[lovasoa]

Maybe Cargo.lock should be committed...

[CryZe]

Nah, you don't commit Cargo.lock for libraries. Then CI would pass but it would still fail to build on 1.28 for everyone depending on this crate. One solution is to depend on cfg-if =0.1.9, but that's probably just causing even more problems, so 1.28 should probably just be dropped.

[LukasKalbertodt]

@fintelia Do you think this fix can be released with a minor version bump (i.e. 0.1.17)? That would be really great, as jpeg-decoder caused 290 other crates to regress due to this. That's the second most regression caused after colored.

[fintelia]

@LukasKalbertodt 0.1.17 has now been published.