refine forward

```
if test:
p0 = torch.nn.functional.pad(f[0], [16, 16, 16, 16])[:, :, 4*pos[0]:4*pos[0]+61, 4*pos[1]:4*pos[1]+61]
p1 = torch.nn.functional.pad(f[1], [8, 8, 8, 8])[:, :, 2 * pos[0]:2 * pos[0] + 31, 2 * pos[1]:2 * pos[1] + 31]
p2 = torch.nn.functional.pad(f[2], [4, 4, 4, 4])[:, :, pos[0]:pos[0] + 15, pos[1]:pos[1] + 15]
else:
p0 = F.unfold(f[0], (61, 61), padding=0, stride=4).permute(0, 2, 1).contiguous().view(-1, 64, 61, 61)
if not (pos is None): p0 = torch.index_select(p0, 0, pos)
p1 = F.unfold(f[1], (31, 31), padding=0, stride=2).permute(0, 2, 1).contiguous().view(-1, 256, 31, 31)
if not (pos is None): p1 = torch.index_select(p1, 0, pos)
p2 = F.unfold(f[2], (15, 15), padding=0, stride=1).permute(0, 2, 1).contiguous().view(-1, 512, 15, 15)
if not (pos is None): p2 = torch.index_select(p2, 0, pos)
```
Can this line ```if not (pos is None): p0 = torch.index_select(p0, 0, pos)``` be deleted because there is no ```pos``` in the training?