Last seen field for Proxy not updated if history cache is overloaded and proxy data throttling is done

Steps to reproduce:

1. install any 5.0/5.4+ version with ZBXNEXT-6503 with proxy (passive/active)
2. reduce history cache
3. break connectivity for proxy for some time to get queue
4. check last seen field for proxy on the server side - it will show minutes of delay, even if the queue reduces when sql used to check proxy backlog

Expected:
Last seen field should be updated even if throttling is done, since where is internal items what will fire up trigger about proxy availability and it's confusing.