Fix session issue on long running requests (#6470)

CHANGELOG

@@ -13,6 +13,7 @@ CHANGELOG Roundcube Webmail
 - Fix support for "allow-from <uri>" in "x_frame_options" config option (#6449)
 - Fix bug where valid content between HTML comments could have been skipped in some cases (#6464)
 - Fix multiple VCard field search (#6466)
+- Fix session issue on long running requests (#6470)
 
 RELEASE 1.3.7
 -------------

program/lib/Roundcube/rcube_session.php

@@ -300,7 +300,7 @@ abstract class rcube_session
             $cache = null;
         }
         // use internal data for fast requests (up to 0.5 sec.)
-        else if ($key == $this->key && (!$this->vars || $ts - $this->start < 0.5)) {
+        else if ($key == $this->key && (!$this->vars || microtime(true) - $this->start < 0.5)) {
             $cache = $this->vars;
         }
         else { // else read data again