make it safer input argument type check in sampling method

[wbaek]

In my case, during T2I sampling

In the part of declaring the following variable
When using as int type like this

top_k=1024
top_p=1

I met the following error message:

object of type 'int' has no len()

[chiheonk]

This is indeed better and LGTM, but this will break the scripts when they are parsing topk, topp from config, in particular:

rq-vae-transformer/main_sampling_fid.py

Lines 72 to 76 in c3de514

	if args.top_k is None:
	args.top_k = config.sampling.top_k
	if args.top_p is None:
	args.top_p = config.sampling.top_p

rq-vae-transformer/main_sampling_txt2img.py

Lines 70 to 74 in c3de514

	if args.top_k is None:
	args.top_k = config.sampling.top_k
	if args.top_p is None:
	args.top_p = config.sampling.top_p

This is due to that args.topk, args.topp is to be omegaconf.ListConfig and when passed to the method sample, type checking will cause error.
So we would need a fix in those scripts to convert ListConfig into list or tuple.