Unexpected result with Resampler.apply for non-naive time index
When resampling a non-naive time series with a custom function (using apply or agg), an unexpected result is returned.

```python
import pandas as pd

def weighted_quantile(series, weights, q):
    series = series.sort_values()
    cumsum = weights.reindex(series.index).fillna(0).cumsum()
    cutoff = cumsum.iloc[-1] * q
    return series[cumsum >= cutoff].iloc[0]

times = pd.date_range('2017-6-23 18:00', periods=8, freq='15T', tz='UTC')
data = pd.Series([1., 1, 1, 1, 1, 2, 2, 0], index=times)
weights = pd.Series([160., 91, 65, 43, 24, 10, 1, 0], index=times)

data.resample('D').apply(weighted_quantile, weights=weights, q=0.5)
```
```
Out[2]: 
2017-06-23 00:00:00+00:00    0.0
Freq: D, dtype: float64
```
#### Expected Output

The (single) value of the series should correspond with:
```python
weighted_quantile(data, weights=weights, q=0.5)
```
```
Out[3]: 1.0
```

One indeed gets this result when passing `data` and `weigths` with naive time index:

```python
times_naive = pd.date_range('2017-6-23 18:00', periods=8, freq='15T')
data = pd.Series([1., 1, 1, 1, 1, 2, 2, 0], index=times_naive)
weights = pd.Series([160., 91, 65, 43, 24, 10, 1, 0], index=times_naive)

data.resample('D').apply(weighted_quantile, weights=weights, q=0.5)
```
```
Out[4]: 
2017-06-23    1.0
Freq: D, dtype: float64
```
But, as shown above, not when passing non-naive time series.


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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.6.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None
pandas: 0.23.4
pytest: 4.2.1
pip: 19.0.2
setuptools: 39.0.1
Cython: 0.29.4
numpy: 1.16.0
scipy: 1.2.0
pyarrow: None
xarray: 0.11.3
IPython: 7.2.0
sphinx: None
patsy: 0.5.1
dateutil: 2.7.5
pytz: 2018.9
blosc: None
bottleneck: 1.2.1
tables: None
numexpr: None
feather: None
matplotlib: 2.2.3
openpyxl: 2.5.12
xlrd: 1.2.0
xlwt: 1.3.0
xlsxwriter: 1.1.2
lxml: 4.3.0
bs4: 4.6.1
html5lib: 1.0.1
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
