BUG: Up-Resample data with PeriodIndex has unexpected behavior
- I have checked that this issue has not already been reported.

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

---

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

```python
import pandas as pd
# Example-1: 
s = pd.Series([1, 2], index=pd.period_range('2012-01-01',
                                            freq='A',
                                            periods=2))
print(s)         
# 2012    1
# 2013    2
# Freq: A-DEC, dtype: int64
                               
print(s.resample('Q', kind='period', convention='start').count())
# 2012Q1    1.0
# 2012Q2    NaN
# 2012Q3    NaN
# 2012Q4    NaN
# 2013Q1    2.0
# 2013Q2    NaN
# 2013Q3    NaN
# 2013Q4    NaN

# Example-2: the result is all NaN, but the data is actually grouped
idx = pd.period_range(start='1/10/2000', periods=2, freq='D')
series = pd.Series(range(2,4), index=idx)
print(series.resample('12H',  convention='end').count())
# 2000-01-10 12:00   NaN
# 2000-01-11 00:00   NaN
# 2000-01-11 12:00   NaN
print(series.resample('12H',  convention='start').count())
# 2000-01-10 00:00    2.0
# 2000-01-10 12:00    NaN
# 2000-01-11 00:00    3.0
# 2000-01-11 12:00    NaN
# Freq: 12H, dtype: float64

for idx, ss in rs: 
    if ss.empty == False: print(ss)
# 2000-01-10    2
# Freq: D, dtype: int64
# 2000-01-11    3
# Freq: D, dtype: int64
```

#### Problem description

Try to up-resample a time series with `PeriodIndex` as the index of the series, and then count the number of records in each time-group. However, the output is not the "count", but it seems to be the only record's value in the group. 

In the second example with `convention='end'`, the result is all `NaN`. If switches to 'convention='start'', then the result is similar to that of the Example-1. In addition, from the grouped details, we can see that the data has been correctly grouped, while the aggregate functions (e.g., `count`) behave unexpected.

#### Expected Output

The number of samples for each group (call the `count()` method).

As a comparison of Example-1, I make another example, which tries to up-sample a time series with `Timestamp` as index. It behaves as expected.

```python
s = pd.Series([1, 2], index=pd.date_range('2012-01-01',
                                            freq='A',
                                            periods=2))
display(s)                                        
# 2012-12-31    1
# 2013-12-31    2
# Freq: A-DEC, dtype: int64

display(s.resample('Q', convention='start').count())
# 2012-12-31    1
# 2013-03-31    0
# 2013-06-30    0
# 2013-09-30    0
# 2013-12-31    1
```

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

<details>

```
INSTALLED VERSIONS
------------------
commit           : c7f7443c1bad8262358114d5e88cd9c8a308e8aa
python           : 3.7.10.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
Version          : 10.0.19041
machine          : AMD64
processor        : Intel64 Family 6 Model 85 Stepping 4, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.None

pandas           : 1.3.1
numpy            : 1.21.1
pytz             : 2021.1
dateutil         : 2.8.2
pip              : 21.2.1
setuptools       : 49.6.0.post20210108
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 3.0.1
IPython          : 7.25.0
pandas_datareader: None
bs4              : None
bottleneck       : 1.3.2
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.4.2
numexpr          : 2.7.3
odfpy            : None
openpyxl         : 3.0.7
pandas_gbq       : None
pyarrow          : 4.0.1
pyxlsb           : None
s3fs             : None
scipy            : 1.7.0
sqlalchemy       : 1.4.22
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None
```

</details>
