Fix typo for bit_depth

[IanButterworth]

@galenlynch this appears to be a typo. Can you confirm?

Evidently our tests aren't covering this branch.

Fixes #313

[codecov]

Codecov Report

Merging #314 (e42c547) into master (7709189) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #314   +/-   ##
=======================================
  Coverage   81.45%   81.45%           
=======================================
  Files          17       17           
  Lines        1181     1181           
=======================================
  Hits          962      962           
  Misses        219      219           

Impacted Files	Coverage Δ
src/avio.jl	81.34% <0.00%> (ø)
src/frame_graph.jl	99.18% <ø> (ø)

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[galenlynch]

Whoops my bad. That is definitely a typo, but the correct value is bit_depth, not padded_bits_per_pixel. I'll make a PR against your branch.

[IanButterworth]

@galenlynch this slipped through. Do you recall if it's still correct? I assume so, but confirmation would be appreciated

[galenlynch]

Hey sorry I've been AWOL. Will check it today.