Reduction bug

[ShuangLiu1992]

in reduction.cpp when dim == 2
clearly there is a bug since b.channel is set to be 1, but in the loop it is assumed to still have the same number of channels as a, as in const float* ptr = a.channel(q); float* outptr = b.channel(q);

    else if (dim == 2)
    {
        // w h c -> X h c
        b.create(h, channels, elemsize, opt.blob_allocator);
    }

    else if (dim == 2)
    {
        #pragma omp parallel for num_threads(opt.num_threads)
        for (int q=0; q<channels; q++)
        {
            const float* ptr = a.channel(q);
            float* outptr = b.channel(q);

            for (int i=0; i<h; i++)
            {
                float sum = v0;
                for (int j=0; j<w; j++)
                {
                    sum = op(sum, ptr[i]);
                }

                outptr[i] = sum * coeff;

                ptr += w;
            }
        }
    }