BUG: Inconsistent results using pd.json_normalize() on a generator object versus list (off by one)
- [ x] I have checked that this issue has not already been reported.

- [ x] I have confirmed this bug exists on the latest version of pandas.

---

#### Code Sample, a copy-pastable example
Only one value is returned with this:

```python
def gen():
    test = [{'created_at': '2020-08-24T09:30:05Z',
             '_id': '5f43889de6a98fd57afce7be'},
            {'created_at': '2020-08-23T11:16:09Z',
             '_id': '5f44b03799944352493d9317'},
           ]
    for val in test:
        yield val
        
results = gen()
pd.json_normalize(results)

```
![image](https://user-images.githubusercontent.com/12517855/91455973-528e3f00-e8b5-11ea-9aa4-84d1aba7fc3c.png)

This returns all values though:
```
results = gen()
list_ = [x for x in results]
pd.json_normalize(list_)
```
And so does this:

```python
def list_():
    final = []
    test = [{'created_at': '2020-08-24T09:30:05Z',
             '_id': '5f43889de6a98fd57afce7be'},
            {'created_at': '2020-08-23T11:16:09Z',
             '_id': '5f44b03799944352493d9317'},
           ]
    for val in test:
        final.append(val)
    return final

results = list_()
pd.json_normalize(results)
```

![image](https://user-images.githubusercontent.com/12517855/91456094-72bdfe00-e8b5-11ea-9d78-e7415b3ef46c.png)


#### Problem description

Using pd.json_normalize() on a generator always seems to reduce the expected results by 1. I first noticed this on a REST API where a column informed me that I should expect 901 results but I kept getting 900 results each time. When I tried to append the results to a list and normalize that, I got the expected 901 results.

#### Expected Output
Perhaps this is an expected output. It just caused me some headaches earlier and it was not immediately obvious that I was missing one record. I would expect that my example above would result in the same 2 row DataFrame.

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

<details>

INSTALLED VERSIONS
------------------
commit           : d9fff2792bf16178d4e450fe7384244e50635733
python           : 3.8.5.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.3.0-1028-azure
Version          : #29~18.04.1-Ubuntu SMP Fri Jun 5 14:32:34 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : en_US.UTF-8
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.0
numpy            : 1.19.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.2.2
setuptools       : 49.6.0.post20200814
Cython           : 0.29.21
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : 2.8.5 (dt dec pq3 ext lo64)
jinja2           : 2.10.3
IPython          : 7.17.0
pandas_datareader: None
bs4              : 4.9.1
bottleneck       : 1.3.2
fsspec           : 0.7.4
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.0
numexpr          : 2.7.1
odfpy            : None
openpyxl         : 3.0.4
pandas_gbq       : None
pyarrow          : 1.0.0
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.2
sqlalchemy       : 1.3.19
tables           : 3.6.1
tabulate         : 0.8.7
xarray           : None
xlrd             : 1.2.0
xlwt             : None
numba            : 0.48.0

</details>
