optimize js loading

Author: Liudon

layouts/partials/extend_head.html

@@ -1,7 +1,9 @@
 <meta name="google-site-verification" content="rJrwFlRtYvRvSMxmD-zlGY6ozg6aDFMkfavno3ms5Ew" />
 <meta name="google-adsense-account" content="ca-pub-4739645989170648">
+{{- if .Content }}
 <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-4739645989170648"
      crossorigin="anonymous"></script>
+{{- end }}
 <!--link rel="stylesheet" href="https://cdn.staticfile.org/lxgw-wenkai-screen-webfont/1.7.0/lxgwwenkaiscreen.min.css" media="print" onload="this.media='all'"-->
 <!-- Google tag (gtag.js) -->
 <!--script async src="https://liudon.com/analytics/js?id=G-G9ZDJQN9E2"></script-->