Zabbix agent re-reads the log file from the first after changing the item key, log[], logrt[] and eventlog[]

Zabbix agent re-reads the log file from the first after changing the item key, log[], logrt[] and eventlog[]. Because when they are saved, the lastlogsize variable is updated to 0. So, Zabbix agent does so.

I attached the patch. It adds the check botton to the WEB frontend to select update lastlogsize or not on Zabbix Active type.