Only set stream status zone if hostname exists (#2684)

Problem: Noticed during conformance tests, the stream server blocks did not have a hostname, and therefore the status_zone value was empty and invalid.

Solution: Only set the status_zone directive if it has a value.

Author: sjberman

internal/mode/static/nginx/config/stream_servers_template.go

@@ -13,7 +13,7 @@ server {
     {{- range $address := $s.RewriteClientIP.RealIPFrom }}
     set_real_ip_from {{ $address }};
     {{- end}}
-	{{- if $.Plus }}
+	{{- if and $.Plus $s.StatusZone }}
     status_zone {{ $s.StatusZone }};
     {{- end }}