failpoint can be actived if it is injected with in a function clusure

[glorv]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error. demo code:

   f := func(g func() error) {}
   f(func() error {
   failpoint.Inject("with-in-a-clusure", func() {
   failpoint.Return(errors.New("mock err"))
   })
   return nil
   })

   exec failpoint-ctl enable, the failpoint.Inject remains unchanged.

2. What did you expect to see?

3. What did you see instead?

4. Versions of the failpoint

[glorv]

duplicated with #70