Do not break if update doesn't have remote_event

drivers/caldav/caldav_driver.php

@@ -2230,6 +2230,12 @@ else {
 
         foreach($updates as $update)
         {
+            if(is_null($update['remote_event'])
+            {
+                self::debug_log("No remote_event in update: ".print_r($update, true));
+                continue;
+
+            }
             if($update['remote_event']['allday'])
             {
                 //caldav has exclusive end dates set to midnight of the next day.