fix(global): zero event previewer mismatch

Author: ibhagwan

lua/fzf-lua/class.lua

@@ -52,7 +52,7 @@ function Object:is(T)
 end
 
 function Object:__tostring()
-  return "Object"
+  return string.format("Object %p", self)
 end
 
 function Object:__call(...)

lua/fzf-lua/previewer/builtin.lua

@@ -474,6 +474,8 @@ function Previewer.base:zero(_)
   local act = string.format("execute-silent(mkdir %s && %s)",
     libuv.shellescape(self._zero_lock),
     shell.stringify_data(function(_, _, _)
+      -- upvalue incase previewer was detached/re-attached (global picker)
+      self = self.win._previewer or self
       vim.defer_fn(function()
         if self.win:validate_preview() then
           self:clear_preview_buf(true)