Fails If Image Not Found

[everythingfunctional]

At lines 169-170, if a suitable image isn't found, the script crashes, since nothing is returned from the get_top_image function in that case. Here's the error message:

Traceback (most recent call last):
  File "./change_wallpaper_reddit.py", line 170, in <module>
    if "url" not in image:
TypeError: argument of type 'NoneType' is not iterable

It's causing problems when trying to change my background hourly with the --time hour option.