fp-SVG's plot() ignores the last past frame + a fix suggestion

[badooki]

Hi,

The plot() function in train_svg_fp.py has an issue of disregarding the last frame of the past frames, before moving on to predicting future frames.

At the end of if i < opt.n_past: block (<for i in range(1, opt.n_eval):<for s in range(nsample):<def plot(x, epoch):) (line 189), I suggest adding the following lines:

h, skip= h_seq[i]
h = h.detach()

With this change the following will happen:
h will be overwritten by h, skip = h_seq[i-1] in line 180, until i < opt.n_past. However, when the loop updates/iterates i from opt.n_past - 1 to opt.n_past, h and skip from the last of the past frames will be used in the else: block starting in line 190.

lp-SVG code does not suffer from this issue, but skip connection still comes from a second last frame of the past frames, which I do not think is a big issue (although may not be ideal).