Fixing Stride Handling for OpenH264

[adamroach]

The golang image.YCbCr struct can contain fields of arbitrary stride
lengths, which don't necessarily match the field widths. This
patch passes the stride values from the image.YCbCr struct into
the OpenH264 encode calls.

[codecov]

Codecov Report

Merging #381 (6d04eb9) into master (e316b30) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #381      +/-   ##
==========================================
+ Coverage   46.39%   46.42%   +0.02%     
==========================================
  Files          67       67              
  Lines        4371     4373       +2     
==========================================
+ Hits         2028     2030       +2     
  Misses       2220     2220              
  Partials      123      123              

Impacted Files	Coverage Δ
pkg/codec/openh264/openh264.go	73.33% <100.00%> (+0.91%)	⬆️

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[Sean-Der]

Thanks @adamroach ! LGTM, I am not intimately familiar with the code base so adding @at-wat just in case.

Happy to merge in a day or two otherwise :)

[at-wat]

LGTM