fix: arithmetic on nil value error on first git project open (#3064)

* fixed error message when opening new git repo

* defensive nil + type check

---------

Co-authored-by: Alexander Courtis <alex@courtis.org>

lua/nvim-tree/explorer/init.lua

@@ -389,9 +389,9 @@ function Explorer:populate_children(handle, cwd, node, project, parent)
           nodes_by_path[child.absolute_path] = true
           child:update_git_status(node_ignored, project)
         end
-      else
+      elseif node.hidden_stats then
         for reason, value in pairs(FILTER_REASON) do
-          if filter_reason == value then
+          if filter_reason == value and type(node.hidden_stats[reason]) == "number" then
             node.hidden_stats[reason] = node.hidden_stats[reason] + 1
           end
         end