Fix a possible count(null) in PHUIInfoView

Summary:
See <https://discourse.phabricator-community.org/t/php7-2-exception-count-parameter-must-be-an-array-or-an-object-that-implements-countable/1031>.

PHP7.2 raises a warning about `count(scalar)` (GREAT!) and we have one here if the caller doesn't `setErrors(...)`.

Test Plan: Sanity-checked usage of `$this->errors`.

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D18964

src/view/phui/PHUIInfoView.php

@@ -10,7 +10,7 @@ final class PHUIInfoView extends AphrontTagView {
   const SEVERITY_PLAIN = 'plain';
 
   private $title;
-  private $errors;
+  private $errors = array();
   private $severity = null;
   private $id;
   private $buttons = array();