TEST: Assert MDL skin width is multiple of four

[MotoLegacy]

Description of Changes

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Doing some digging trying to produce failure for the bad mesh in nzp-team/nzportable#1194 I found some additional safe guards that some early Quake engines have with the skin width required to be a multiple of four. While height can be arbitrarily set this way (and we do so on quite a few models, this probably should be revisited) width cannot behave this way. So I added a check to safeguard against this which fails on our broken model.

Visual Sample

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[INFO]: Verifying MDL model [./common/broken_mesh.mdl]..
  + MAGIC: [IDPO]
  + VERSION: [6]
  + SKIN WIDTH: [127]
    - ERROR: Skin width is not multiple of four!
  + SKIN HEIGHT: [59]
  + VERTICES: [113]
  + TRIANGLES: [174]
  + FRAMES: [47]
  - ERROR: Invalid header for MDL [./common/broken_mesh.mdl]!
[ERROR]: FAILED to validate [1] MDL models!

Checklist

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• I have thoroughly tested my changes to the best of my ability
• I confirm I have not contributed anything that would impact Nazi Zombies: Portable's licensing and usage
• This Pull Request fixes a critical issue that should be reviewed and merged as soon as possible