Fix new clippy warnings

[codecov[bot]]

Codecov Report

Merging #80 (30ee435) into prīmum (de91866) will decrease coverage by 1.61%. The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           prīmum      #80      +/-   ##
==========================================
- Coverage   72.49%   70.87%   -1.62%     
==========================================
  Files           7        7              
  Lines         309      309              
==========================================
- Hits          224      219       -5     
- Misses         85       90       +5     

Impacted Files	Coverage Δ
src/decode.rs	61.17% <33.33%> (-2.36%)	:arrow_down:
src/encode.rs	80.85% <100.00%> (-2.13%)	:arrow_down:
src/alphabet.rs	52.77% <0.00%> (-2.78%)	:arrow_down:

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[Nemo157]

bors r+

[bors[bot]]

Build succeeded:

• cargo audit
• cargo clippy
• cargo doc --cfg docsrs
• cargo fmt --check
• cargo hack check --feature-powerset
• cargo test
• cargo test --shallow-minimal-versions
• cargo test (stable, i686-pc-windows-msvc, windows-latest)
• cargo test (stable, i686-unknown-linux-gnu, ubuntu-latest)
• cargo test (stable, x86_64-apple-darwin, macos-latest)
• cargo test (stable, x86_64-pc-windows-msvc, windows-latest)
• cargo test (stable, x86_64-unknown-linux-gnu, ubuntu-latest)