fix(fs): error when plugin directory to delete is not a valid directory

Author: folke

lua/lazy/manage/task/fs.lua

@@ -13,7 +13,7 @@ M.clean = {
     assert(dir:find(Config.options.root, 1, true) == 1, self.plugin.dir .. " should be under packpath!")
 
     local stat = vim.loop.fs_lstat(dir)
-    assert(stat.type == "directory", self.plugin.dir .. " should be a directory!")
+    assert(stat and stat.type == "directory", self.plugin.dir .. " should be a directory!")
 
     Util.walk(dir, function(path, _, type)
       if type == "directory" then