user/%/spambot should support lookup by username or UID

The user/%/spambot page looks up which user to work on by using the user_load_by_name() function, which means it works great with URLs like "user/username/spambot", but not so well with "user/123/spambot". The latter, however, is how the tab is being linked from user pages on my site, which means that when I click the link I get the standard "Anonymous user can't be reported" error.

This could be resolved by adding an additional check —if user_load_by_name() fails, simply call user_load() and see if that works. If not, continue on through to the error as happens currently.