fix(findmydevice): Fix SLO error query

apps/k8s01/findmydevice/slo.yaml

@@ -11,7 +11,7 @@ spec:
       description: "Find My Device: SLO based on availability for HTTP request responses."
       sli:
         events:
-          errorQuery: sum(rate(nginx_ingress_controller_requests{exported_namespace="findmydevice",ingress="fmd-findmydevice",status=~"(5..|429)"}[{{.window}}]))
+          errorQuery: sum(rate(nginx_ingress_controller_requests{exported_namespace="findmydevice",ingress="fmd-findmydevice",status=~"(5..|429)"}[{{.window}}])) OR vector(0)
           totalQuery: sum(rate(nginx_ingress_controller_requests{exported_namespace="findmydevice",ingress="fmd-findmydevice"}[{{.window}}])) > 0 OR vector(1)
       alerting:
         name: FMDHighErrorRate