Fix check condition to avoid timeouts in invalid panels

[spinillos]

When we are trying to render a panel that isn't able to retrieve the information from the datasource, panelsRendered never exists.

It means, that we are waiting to fit a condition that is never met. For this reason, image renderer waiting until the timeout is reached.

Checking if panelsRendered exists, takes the screenshot of the invalid panel avoiding the timeout.

[CLAassistant]

All committers have signed the CLA.