Fix leak when an async fs_scandir request has an error

src/fs.c

@@ -256,6 +256,13 @@ static int push_fs_result(lua_State* L, uv_fs_t* req) {
   }
 
   if (req->result < 0) {
+    if (req->fs_type == UV_FS_SCANDIR) {
+      // We need to unref the luv_fs_scandir_t userdata to allow it to be garbage collected.
+      // The scandir callback can only be called once, so we now know that the
+      // req can be safely garbage collected.
+      luaL_unref(L, LUA_REGISTRYINDEX, data->data_ref);
+      data->data_ref = LUA_NOREF;
+    }
     lua_pushnil(L);
     if (fs_req_has_dest_path(req)) {
       lua_rawgeti(L, LUA_REGISTRYINDEX, data->data_ref);

tests/manual-test-leaks.lua

@@ -54,6 +54,15 @@ return require('lib/tap')(function (test)
     end)
   end)
 
+  test("fs-scandir-async error", function (print, p, expect, uv)
+    bench(uv, p, 0x10000, function ()
+      local outer_req = assert(uv.fs_scandir('intentionally missing folder this should not exist!', function(err, req)
+        assert(err)
+        assert(not req)
+      end))
+    end)
+  end)
+
   test("lots-o-timers", function (print, p, expect, uv)
     bench(uv, p, 0x100000, function ()
       local timer = uv.new_timer()