bug， using sliding eval with batch size larger than 1 on each gpu

[fuchangjie]

evaluate.py in branch pytorch-1.1 line 134 and line 135 you only use the prediction result of the first image, but treat it as the result of the remaining images in the same batch, in line 136. so something goes wrong when evaluate with batch size larger than 1. you should modify it with prediction = padded_prediction[:, 0:img.shape[2], 0:img.shape[3], :] and count_predictions[:, y1:y2, x1:x2] += 1

[ybchen97]

@fuchangjie Hey, thank you so much for finding this bug!

[ironcadiz]

I wrote #55 like a year ago addressing this