Rx2day, Rx5day resulting in some infinite values
Two extreme precipitation indices, `rx2day` and `rx5day`, produces some infinite values on e.g. GridClim and PTHBV datasets. For both these datasets there are no issues with `rx1day`.
Example (on bi):
```python
import iris
from climix.metadata import load_metadata
from dask.distributed import Client
client = Client()
fname = "/nobackup/rossby26/users/sm_erhol/extremeEventAttribution/gavle2021/pr_gavle2021_SMHIGridClim_day_19610101-20181230.nc"
# This will be an masked array
cube = iris.load_cube(fname)
index_catalogue = load_metadata()
index = index_catalogue.prepare_indices(["rx2day"])[0]
index_cube = index([cube], client)
assert not np.any(np.isinf(index_cube.data))
```
When realising the `index_cube` some overflow warnings are thrown. If the spatial dimensions of the cube are collapsed (average, max), no infinite values are produced.
issue