Overriding default dimensions import setting on a VideoClip can mess up if you mix a 'Square' dimension with a half/quarter/full resolution dimension.

Steps to reproduce:
1. Download project: https://oc.unity3d.com/index.php/s/Ds1Nr2IfXpkWMMQ
2. Modify WinterWonderland_VideoClip to have transcoding enabled by default.
3. Set the default dimensions value to 'Original'
4. Click on a different platform (for example, iOS or Android) and enable an import override
5. Enable transcoding here too, and specify Dimensions to be 'Square 512x512'
6. Apply settings
7. Switch to the platform you overrode in the build settings (e.g. iOS / Android)
8. Observe video is not square in the inspector