length_of_indexer method is not support boolean array indexer.
#### Code Sample

```python
import numpy as np
import pandas as pd
import random

# Nothing Raises
df = pd.DataFrame(dict(A=[1, 1, 1, 1, 1], B=[1., 1., 1., 1., 1.], C=[1, 1, 1, 1, 1]))
df.index = [0, 0, 1, 3, 5]
df.index.name = 'test'
df.loc[0, 'A'] = df.loc[0, 'A']

# ValueError raises
length = 20000
df = pd.DataFrame(dict(A=[1 for _ in range(length)], B=[1. for _ in range(length)], C=[1 for _ in range(length)]))
index = []
for _ in range(length):
    index.append(random.randint(0, 2000))
df.index = index
df.loc[0, 'A'] = df.loc[0, 'A']
```
#### Problem description

https://github.com/pandas-dev/pandas/blob/db6993cdd970eb13790493dba38bb637e341948b/pandas/core/indexing.py#L517

https://github.com/pandas-dev/pandas/blob/db6993cdd970eb13790493dba38bb637e341948b/pandas/core/indexing.py#L546-L562

When the `DataFrame.loc` method uses boolean array selector in the backgroud, the variable `lplane_indexer` is not the same value as the number of True value in the array but the size of DataFrame. It didn't happen in a former version.

#### Expected Output

No error raises.

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.7.final.0
python-bits: 64
OS: Linux
OS-release: 4.15.0-46-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.3
pytest: 3.7.3
pip: 18.1
setuptools: 36.5.0.post20170921
Cython: 0.28.4
numpy: 1.15.4
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 7.2.0
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.3
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.4
feather: None
matplotlib: 3.0.2
openpyxl: None
xlrd: 1.2.0
xlwt: None
xlsxwriter: 1.1.5
lxml: None
bs4: 4.6.0
html5lib: 1.0.1
sqlalchemy: 1.2.10
pymysql: 0.9.3
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None


</details>
