Anonymous user (0) has many associated accounts because of twitter_fetch_mentions_timeline()

When twitter_fetch_mentions_timeline() encounters a mention, it will save the author of that tweet in the twitter_account table with uid = 0, which is the anonymous user. When user_load(0) is called, twitter_user_load() will happily load all twitter accounts with uid = 0, which can be a lot. I suggest that twitter_user_load() is changed such that it will not process uid = 0.