Choose a thumbnail from the photos of the post without thumbnail and banner

Signed-off-by: Xiaofeng QU <xiaofeng.qu.hk@ieee.org>

layout/_partial/post/thumbnail.ejs

@@ -6,6 +6,8 @@
       s = post.thumbnail;
     }else if (post.banner){
       s = post.banner;
+    }else if (post.photos && post.photos.length){
+      s = post.photos[0];
     }else{
       var img=/\<img\s.*?\s?src\s*=\s*['|"]?([^\s'"]+).*?\>/ig;
       var result = post.content.match(img);