BUG: value_counts can handle the case even with empty groups (#28479)
* If applying rep to recons_labels go fail, use ids which has no
  consecutive duplicates instead. 

- [x] closes #28479 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

xuancong84 found that value_counts() crashes if `groupby` object contains empty groups.
However, even though I made the construction of DataFrame don't skip empty rows, it still crashed.
Till then, I already tried in many ways though, in this time I tried to correct the callee `self.grouper.recons_labels`. After several tests, I found that If freq of `Grouper` is too long so that it has empty groups in some periods then it crashes. And also have found that this is solved by using `ids` which has no consecutive duplicates instead of `self.grouper.recons_labels`.
Why did they go fail..?? I have never changed any contents of test_categorical.py though... and apart from me, he also has the same problem. https://github.com/pandas-dev/pandas/pull/28595

Is there any problem with CI now? I closed this issue because of CI issues