BUG: Pandas Cython pd.sort_values() function, ignore_index DOESN'T WORK
- [ ] I have checked that this issue has not already been reported.
yes
- [ ] I have confirmed this bug exists on the latest version of pandas.
yes
- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.
idk
<img width="646" alt="Capture d’écran 2020-05-07 à 00 12 24" src="https://user-images.githubusercontent.com/60808981/81234096-635e3080-8ff8-11ea-9f53-3c9709a66f34.png">




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**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
# Your code here

```

#### Problem description
The code works on python3, but not on Cython. It works when I delete "ignore_index=True" from my code, but then the output is obviously wrong :(
(sorry for censoring, I don't want to leak anything)
[this should explain **why** the current behaviour is a problem and why the expected output is a better solution]

#### Expected Output
ignore_index should work on Cython 
#### Output of ``pd.show_versions()``
1.0.3
<details>

[paste the output of ``pd.show_versions()`` here leaving a blank line after the details tag]

</details>