fs: fix watchFile() missing deletion events

Make sure the deletion event gets reported in the following scenario:

  1. Watch a file.
  2. The initial stat() goes okay.
  3. Something deletes the watched file.
  4. The second stat() fails with ENOENT.

The second stat() translates into the first 'change' event but a logic error
stopped it from getting emitted.

Fixes #4027.