BUG: Arithmetic operations on 0 length ExtensionArrays aren't tested
pint-pandas includes the arithmetic tests, but had an issue opened for performing addition on a 0 length PintArray. I don't think this is tested in the EA tests.

```
import pint_pandas 
import numpy as np
import pint
import pandas as pd

PA_= pint_pandas.PintArray
PT_ = pint_pandas.PintType
ureg=pint.get_application_registry()

data = PA_.from_1darray_quantity(
        np.arange(start=1.0, stop=101.0) * ureg.nm
    )
s = pd.Series(data)
s.loc[[]] + (1 * ureg.meter) # Untested
```