Fixed bug on incorrect date format for 1970-01-01 date. (#3802)

Author: kiatng

app/code/core/Mage/Core/Helper/Data.php

@@ -162,7 +162,7 @@ public function formatDate($date = null, $format = Mage_Core_Model_Locale::FORMA
         } elseif (is_int($date)) {
             $date = Mage::app()->getLocale()->date($date, null, null, $useTimezone);
         } elseif (!$date instanceof Zend_Date) {
-            if ($time = strtotime($date)) {
+            if (($time = strtotime($date)) !== false) {
                 $date = Mage::app()->getLocale()->date($time, null, null, $useTimezone);
             } else {
                 return '';

app/code/core/Mage/Core/Model/Locale.php

@@ -518,7 +518,7 @@ public function date($date = null, $part = null, $locale = null, $useTimezone =
             $locale = $this->getLocale();
         }
 
-        if (empty($date)) {
+        if (!is_int($date) && empty($date)) {
             // $date may be false, but Zend_Date uses strict compare
             $date = null;
         }