DecodeAllMipMaps2D(DdsFile) returns empty array if dwMipMapCount is 0 even when there is a face with mip maps

[Crauzer]

This issue arises from the fact that mip count is handled differently in DdsFile and in DecodeInternal.

These are the relevent lines:
https://github.com/Nominom/BCnEncoder.NET/blob/master/BCnEnc.Net/Decoder/BcDecoder.cs#L1161-L1164
https://github.com/Nominom/BCnEncoder.NET/blob/master/BCnEnc.Net/Shared/ImageFiles/DdsFile.cs#L57

I think the easiest way to fix this would to be assume that each file has at least 1 mipmap. Microsoft says that you shouldn't rely on the mipmap flag being set.

[Crauzer]

Another reference to mip count being clamped to at least 1:
https://learn.microsoft.com/en-us/windows/uwp/gaming/complete-code-for-ddstextureloader

    size_t mipCount = header->mipMapCount;
    if (0 == mipCount)
    {
        mipCount = 1;
    }