Fix so microseconds macro (u) in log_date_format works (#1490446)

CHANGELOG

@@ -5,6 +5,7 @@ CHANGELOG Roundcube Webmail
 - Fix regression where groups with email address were resolved to its members' addresses
 - Fix so group/addressbook selection is retained on page refresh
 - Fix bug where signature couldn't be added above the quote in Firefox 51 (#5628)
+- Fix so microseconds macro (u) in log_date_format works (#1490446)
 
 RELEASE 1.1.7
 -------------

program/lib/Roundcube/rcube.php

@@ -1277,11 +1277,7 @@ class rcube
             $session_key = intval(self::$instance->config->get('log_session_id', 8));
         }
 
-        if (empty($date_format)) {
-            $date_format = 'd-M-Y H:i:s O';
-        }
-
-        $date = date($date_format);
+        $date = rcube_utils::date_format($date_format);
 
         // trigger logging hook
         if (is_object(self::$instance) && is_object(self::$instance->plugins)) {

program/lib/Roundcube/rcube_utils.php

@@ -1178,4 +1178,27 @@ class rcube_utils
 
         return $random;
     }
+
+    /**
+     * Format current date according to specified format.
+     * This method supports microseconds (u).
+     *
+     * @param string $format Date format (default: 'd-M-Y H:i:s O')
+     *
+     * @return string Formatted date
+     */
+    public static function date_format($format = null)
+    {
+        if (empty($format)) {
+            $format = 'd-M-Y H:i:s O';
+        }
+
+        if (strpos($format, 'u') !== false
+            && ($date = date_create_from_format('U.u.e', microtime(true) . '.' . date_default_timezone_get()))
+        ) {
+            return $date->format($format);
+        }
+
+        return date($format);
+    }
 }