Minor improvement for array value linter rule
This linter rule fails on multi-line arrays with no whitespace before the first array value. Specifically, the following exception is thrown:
Fatal error: Call to a member function isAnyWhitespace() on boolean in arcanist/src/lint/linter/xhpast/rules/ArcanistArrayValueXHPASTLinterRule.php on line 40
Test Plan: Added another test case.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Differential Revision: https://secure.phabricator.com/D13856