REGR: bug in moments when using bottleneck
closes #16116

Do `nanskew`, `nankurt`, and `nansem` need the same fix too? done (``nansem`` already hits the ``nanvar`` path).

I had changed this code a long time ago (but in 0.20.0) IIRC to simplify. Guess was not fully exercised. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=h1) Report
> Merging [#16124](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4ca4fca839ced3483f37b3ae2434033e2721e1d5?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16124/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16124      +/-   ##
==========================================
+ Coverage   90.83%   90.84%   +<.01%     
==========================================
  Files         159      159              
  Lines       50771    50774       +3     
==========================================
+ Hits        46120    46124       +4     
+ Misses       4651     4650       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.62% <100%> (ø)` | :arrow_up: |
| #single | `40.33% <0%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/nanops.py](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbmFub3BzLnB5) | `98.18% <100%> (+0.01%)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.03% <0%> (+0.34%)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=footer). Last update [4ca4fca...15afc09](https://codecov.io/gh/pandas-dev/pandas/pull/16124?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
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