Martin Storsjö e8cdbd2ea7 Don't downsample to anything smaller than 4x4 pixels
This makes for a chroma plane of 2x2. The SIMD versionf of generic
downscalers assume that the width and height is at least 2, since
it does an unconditional loop for the body of the image, and a
separate step for the last pixel and last row. The SIMD versions
assume that (width-1) and (height-1) are larger than zero.

This fixes spurious crashes in EncodeDecodeTestAPI.SetOptionEncParamExt.
2015-02-28 14:58:53 +02:00
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