BUG: reset_index after a group_by raise a ValueError for empty dataframe
### 

- [X] I have checked that this issue has not already been reported.

- [X] I have confirmed this bug exists on the [latest version](https://pandas.pydata.org/docs/whatsnew/index.html) of pandas.

- [ ] I have confirmed this bug exists on the master branch of pandas.


### Reproducible Example

```python
import pandas as pd
import datetime as dt

df = pd.DataFrame([(dt.date.today(), "b", 12)], columns=["date", "b", "count"])
df["date"] = pd.to_datetime(df["date"])
df = df[df["count"] == 1]  # uncomment this line to make the dataframe empty and so reset_index raising an exception
df2 = df.set_index('date').groupby(['b']).resample('M').sum().reset_index()
```


### Issue Description

When you run the code above, df won’t be empty and the code will run correctly. But if you uncomment the line that makes the dataframe empty, the reset index will raise a ValueError(f"cannot insert b, already exists").

This is a regression as it was working in pandas 1.2.x

### Expected Behavior

It’s expected for the reset_index to apply correctly on an empty dataframe too.

### Installed Versions

INSTALLED VERSIONS
------------------
commit           : 73c68257545b5f8530b7044f56647bd2db92e2ba
python           : 3.9.7.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 20.6.0
Version          : Darwin Kernel Version 20.6.0: Mon Aug 30 06:12:21 PDT 2021; root:xnu-7195.141.6~3/RELEASE_X86_64
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.UTF-8
pandas           : 1.3.3
numpy            : 1.21.2
pytz             : 2021.1
dateutil         : 2.8.2
pip              : 21.1.2
setuptools       : 57.0.0
Cython           : None
pytest           : 6.2.5
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : 2.9.1 (dt dec pq3 ext lo64)
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : 1.7.1
sqlalchemy       : 1.4.25
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None