porting PHRAS-1770 to 4.1

lib/classes/record/preview.php

@@ -431,6 +431,7 @@ class record_preview extends record_adapter
             $nbDays--;      // because 0 is included
             for ($d=$nbDays; $d>=0; $d--) {
                 $datetime = new DateTime('-' . $d . ' days');
+                $datetime->modify('+1 day');
                 $date = date_format($datetime, 'Y-m-d');
                 if($d == $nbDays) {
                     $this->statistics['from'] = $date;