chore: Factor out duplicate checks for `default.crt`

for improved readability.

nginx.tmpl

@@ -11,6 +11,7 @@
 {{- $_ := set $globals "Env" $.Env }}
 {{- $_ := set $globals "Docker" $.Docker }}
 {{- $_ := set $globals "CurrentContainer" (where $globals.containers "ID" $globals.Docker.CurrentContainerID | first) }}
+{{- $_ := set $globals "default_cert_ok" (and (exists "/etc/nginx/certs/default.crt") (exists "/etc/nginx/certs/default.key")) }}
 {{- $_ := set $globals "external_http_port" (coalesce $globals.Env.HTTP_PORT "80") }}
 {{- $_ := set $globals "external_https_port" (coalesce $globals.Env.HTTPS_PORT "443") }}
 {{- $_ := set $globals "sha1_upstream_name" (parseBool (coalesce $globals.Env.SHA1_UPSTREAM_NAME "false")) }}
@@ -355,7 +356,7 @@ server {
     {{ $globals.access_log }}
     return 503;
 
-{{- if (and (exists "/etc/nginx/certs/default.crt") (exists "/etc/nginx/certs/default.key")) }}
+{{- if $globals.default_cert_ok }}
     listen {{ $globals.external_https_port }} ssl http2;
     {{- if $globals.enable_ipv6 }}
     listen [::]:{{ $globals.external_https_port }} ssl http2;
@@ -558,7 +559,7 @@ server {
     {{- end }}
 }
 
-    {{- if and (or (eq $https_method "nohttps") (not $cert_ok)) (exists "/etc/nginx/certs/default.crt") (exists "/etc/nginx/certs/default.key") }}
+    {{- if and (or (eq $https_method "nohttps") (not $cert_ok)) $globals.default_cert_ok }}
 server {
     server_name {{ $host }};
         {{- if $server_tokens }}