Alerts from hidden panels

### What Grafana version are you using?
Version 5.0.1 (commit: a747ec3)
### What datasource are you using?
influxdb
### What OS are you running grafana on?
gentoo

Hi,
Alerts on hidden panel didnt work((

I make new alert on graph and save dashboard - all alerts works.

When I collapse row with that graph and save dashboard - alerts from it didn't work.
