Make TestCase::hasOutput() return true if "0" is outputted

TestCase::hasOutput() returns false when "0" is outputted, as it uses empty(), which returns false on the string "0".

Author: dave1010

PHPUnit/Framework/TestCase.php

@@ -393,7 +393,7 @@ public function getActualOutput()
      */
     public function hasOutput()
     {
-        if (empty($this->output)) {
+        if (strlen($this->output) === 0) {
             return FALSE;
         }