Make $this->args consistently available in hook_views_pre_view()

hook_views_pre_view() gets $view, $display_id, $args as an argument.

When the view is rendered normally, the arguments are available in $view->args but not the $args argument.

When the same view is rendered via views_ajax(), the arguments are available in the $args argument, but not in $view->args.

So.. in $view->preview, I moved the ->set_arguments() call up above the hook invoke, and also made the $view->args the argument value, instead of $args. This way, both possible sources are populated correctly in both situations.