fix: incorrect array length in mergeAlignedData

[tobikris]

We had the same issue as #1130. I tried to find the minimum reproducible example:

apiVersion: pyrra.dev/v1alpha1
kind: ServiceLevelObjective
metadata:
  name: prometheus-api-query
  namespace: monitoring
  labels:
    prometheus: k8s
    role: alert-rules
spec:
  target: "99.0"
  window: 7d
  indicator:
    ratio:
      errors:
        metric: prometheus_http_requests_total{handler=~"/.*", code=~"5.."}
      total:
        metric: prometheus_http_requests_total{handler=~"/.*"}

Adding the handler to the example SLO triggers the issue on every UI load for me.

I don't fully understand the code, but I guess that the logic can be improved in a better way to not rely on the hacky loop extending the array just enough.

Anyway, I wanted to share my finding and a workaround at least.