BUG: ExtensionArray TestMethods.test_where_series
- [x] I have checked that this issue has not already been reported.

- [ ] I have confirmed this bug exists on the latest version of pandas.
I'm working on updating pint-pandas to 0.25.1 before the latest version...
- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

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

<details>

```python
TypeError                                 Traceback (most recent call last)
c:\users\a\repos\pint\pint\quantity.py in __getitem__(self, key)
   1737         try:
-> 1738             return type(self)(self._magnitude[key], self._units)
   1739         except PintTypeError:

TypeError: 'float' object is not subscriptable

During handling of the above exception, another exception occurred:

TypeError                                 Traceback (most recent call last)
<ipython-input-14-67c12fe72115> in <module>
----> 1 self.test_where_series(data, na_value, as_frame)

c:\users\a\repos\pint-pandas\pintpandas\test_pandas_interface.py in test_where_series(self, data, na_value, as_frame)
    266             cond = cond.reshape(-1, 1)
    267 
--> 268         result = ser.where(cond)
    269         expected = pd.Series(
    270             cls._from_sequence([a, a, na_value, na_value], dtype=data.dtype)

~\anaconda3\envs\py37_pd251\lib\site-packages\pandas\core\generic.py in where(self, cond, other, inplace, axis, level, errors, try_cast)
   9274         other = com.apply_if_callable(other, self)
   9275         return self._where(
-> 9276             cond, other, inplace, axis, level, errors=errors, try_cast=try_cast
   9277         )
   9278 

~\anaconda3\envs\py37_pd251\lib\site-packages\pandas\core\generic.py in _where(self, cond, other, inplace, axis, level, errors, try_cast)
   9121                 errors=errors,
   9122                 try_cast=try_cast,
-> 9123                 axis=block_axis,
   9124             )
   9125 

~\anaconda3\envs\py37_pd251\lib\site-packages\pandas\core\internals\managers.py in where(self, **kwargs)
    555 
    556     def where(self, **kwargs):
--> 557         return self.apply("where", **kwargs)
    558 
    559     def setitem(self, **kwargs):

~\anaconda3\envs\py37_pd251\lib\site-packages\pandas\core\internals\managers.py in apply(self, f, axes, filter, do_integrity_check, consolidate, **kwargs)
    436                     kwargs[k] = obj.reindex(b_items, axis=axis, copy=align_copy)
    437 
--> 438             applied = getattr(b, f)(**kwargs)
    439             result_blocks = _extend_blocks(applied, result_blocks)
    440 

~\anaconda3\envs\py37_pd251\lib\site-packages\pandas\core\internals\blocks.py in where(self, other, cond, align, errors, try_cast, axis)
   2005             set_other = other
   2006         else:
-> 2007             set_other = other[icond]
   2008         try:
   2009             result[icond] = set_other

c:\users\a\repos\pint\pint\quantity.py in __getitem__(self, key)
   1742             raise TypeError(
   1743                 "Neither Quantity object nor its magnitude ({})"
-> 1744                 "supports indexing".format(self._magnitude)
   1745             )
   1746 

TypeError: Neither Quantity object nor its magnitude (nan)supports indexing

```
</details>

#### Problem description

I'm having trouble with this test as pandas is trying to index into a scalar. I believe this is because this line returns false:
https://github.com/pandas-dev/pandas/blob/185a654e3db9976d33e7ba10b9c464214e7bf280/pandas/core/internals/blocks.py#L1831

```python3
import pintpandas
import matplotlib.pyplot as plt
import numpy as np
import pint
import pandas as pd

ureg=pint.UnitRegistry()
PA_= pintpandas.PintArray
PT_ = pintpandas.PintType
PT_.ureg = ureg
Q_=ureg.Quantity

from pandas._libs import NaT, lib, tslib, tslibs

lib.is_scalar(Q_(1,'m'))
False
```

#### Expected Output

```python3

lib.is_scalar(Q_(1,'m'))
True
```

#### Output of ``pd.show_versions()``

<details>


INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.7.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
machine          : AMD64
processor        : AMD64 Family 23 Model 8 Stepping 2, AuthenticAMD
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.None

pandas           : 0.25.1
numpy            : 1.18.1
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 46.1.3.post20200330
Cython           : 0.29.15
pytest           : 5.4.1
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : 7.13.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : 3.2.1
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
</details>
