修复给分享的文件赋予了全部权限问题 (#260)

core/class/perm/perm_check.php

@@ -161,7 +161,7 @@ class perm_check{
     //$arr=array('uid','gid','desktop');其中这几项必须
     function checkperm($action,$arr,$bz=''){ //检查某个图标是否有权限;
         global $_G;
-        if ($arr['preview']) {
+        if ($arr['preview'] && ($action=='read') || $action=='copy' || $action=='download') {
             return true;
         }
         if($_G['uid']<1){ //游客没有权限