gluon-status-page-api: upgrade: don't throw error messages without rpcd

package/gluon-status-page-api/files/lib/gluon/upgrade/500-status-page-api

@@ -12,4 +12,6 @@ uci -q batch <<-EOF
 	set uhttpd.main.max_requests=32
 EOF
 
-/etc/init.d/rpcd disable
+if [ -x /etc/init.d/rpcd ]; then
+	/etc/init.d/rpcd disable
+fi