generate_sequence_video.py: Add one condition to filter out files

[flyzenr]

Question: There are one or more files in the video_output directory, and their names are not pure numbers or the file names start with a dot (.), e.g., hidden files or non-image files.

Resolution: - Modified script to handle filenames more robustly. For example, add some conditions to filter out files that don't match the naming rules.

img_idx = sorted([int(x.split(".")[0]) for x in os.listdir(seq_out_dir) if x.split(".")[0].isdigit()])