Typecho 图片格式 Webp 格式显示修复

修改了5个文件，修复文件打包下载

modified:   var/Typecho/Common.php
modified:   var/Widget/Abstract/Contents.php
modified:   var/Widget/Options.php
modified:   var/Widget/Options/General.php
modified:   var/Widget/Themes/List.php