Metrics don't render when one environment doesn't have deployments

Zendesk: https://gitlab.zendesk.com/agent/tickets/118916

Customer is using Kubernetes and Prometheus and is trying to get the environment metrics to show. They had a dev, staging and production environment, although production had no deployments yet. The metrics page showed no metrics even for dev and staging, which had deployments.

Customer removed the production environment and the metrics then showed for dev and staging.

The metrics page should handle environments with no deployments and still show metrics for environments with deployments.