Views argument validators don't fire when the argument is 0 due to PHP == insanity

While working on #377566: Hide the "My projects" page for anonymous users I discovered a bug where my views argument validator wasn't getting invoked when the view had an argument value of 0. I thought it was an evil interaction of default arguments not getting the arg validator invoked. However, Earl and I just tracked this down to a bug in views_handler_argument::is_wildcard(). Thanks to the joys of PHP's == operator insanity, 0 == 'all' evaluates to TRUE. Yay!!! Patch coming in a second, stay tuned.