Temporary fix for post_filter() AttributeError

BugFix: post_filter sometimes raises the following error:

Traceback (most recent call last):
    File "./main.py", line 247, in <module>
        main()
    File "./main.py", line 207, in main
        if post_filter(reddit, reddit_post, done_file, done_list) is False:
    File "./main.py", line 103, in post_filter
        elif post.author.name == reddit.user.name:
AttributeError: 'NoneType' object has no attribute 'name'

This commit catches the error as an exception and skips the post.
A better solution is needed.