Fix an error in calculating SIFID

[DonghweeYoon]

I got the same issue with #155.

In the current code, the SIFID is calculated from the activation before the first pooling layer.
To calculate the SIFID as described in the paper, the following modifications are required.

SinGAN/SIFID/inception.py

Line 53 in 286d3cd

self.last_needed_block = max(output_blocks)

If 'dims' is set to 64, 'self.last_needed_block' is set to 0.

SinGAN/SIFID/inception.py

Lines 62 to 79 in 286d3cd

	# Block 0: input to maxpool1
	block0 = [
	inception.Conv2d_1a_3x3,
	inception.Conv2d_2a_3x3,
	inception.Conv2d_2b_3x3,
	]
	self.blocks.append(nn.Sequential(*block0))
	# Block 1: maxpool1 to maxpool2
	if self.last_needed_block >= 1:
	block1 = [
	nn.MaxPool2d(kernel_size=3, stride=2),
	inception.Conv2d_3b_1x1,
	inception.Conv2d_4a_3x3,
	]
	self.blocks.append(nn.Sequential(*block1))

Then the input feature map only passed through 'block0'.
It doesn't go through the first max-pooling layer.