fix the bug-[local variable 'iter_ref' referenced before assignment]

[Johnson-yue]

it report StopIteration Error

[iPsych]

@yunjey with latest source, I am facing same error.
Below is full log

Preparing DataLoader for the evaluation phase...
Preparing DataLoader for the evaluation phase...
100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 22/22 [00:02<00:00, 8.97it/s]
100%|███████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 2/2 [00:00<00:00, 4.06it/s]
Calculating evaluation metrics...
Number of domains: 4
Preparing DataLoader for the evaluation phase...
Preparing DataLoader for the evaluation phase...
Generating images and calculating LPIPS for Happy2Fear...
0%| | 0/1 [00:00<?, ?it/s]
Traceback (most recent call last):
File "/home/ipsych/ML/stargan-v2/metrics/eval.py", line 76, in calculate_metrics
x_ref = next(iter_ref).to(device)
UnboundLocalError: local variable 'iter_ref' referenced before assignment

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "main.py", line 182, in
main(args)
File "main.py", line 59, in main
solver.train(loaders)
File "/home/ipsych/ML/stargan-v2/core/solver.py", line 171, in train
calculate_metrics(nets_ema, args, i+1, mode='reference')
File "/home/ipsych/.conda/envs/Pytorch_1_4_0/lib/python3.7/site-packages/torch/autograd/grad_mode.py", line 49, in decorate_no_grad
return func(*args, **kwargs)
File "/home/ipsych/ML/stargan-v2/metrics/eval.py", line 79, in calculate_metrics
x_ref = next(iter_ref).to(device)
File "/home/ipsych/.conda/envs/Pytorch_1_4_0/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 345, in next
data = self._next_data()
File "/home/ipsych/.conda/envs/Pytorch_1_4_0/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 831, in _next_data
raise StopIteration
StopIteration
I trained with custom dataset named EMO-S consists of four domains with below codes.

python main.py --mode train --num_domains 4 --w_hpf 0 --lambda_reg 1 --lambda_sty 1 --lambda_ds 3 --lambda_cyc 1 --train_img_dir ./data/EMO-S/train --val_img_dir ./data/EMO-S/val

[doantientai]

The line iter_ref = iter(loader_ref) should be inside the condition if mode == 'reference'. Otherwise, it will crash the program because loader_ref is used before being defined.