Integral reductions wrongly error on empty location list

[seanpearsonuk]

An average of a quantity over an empty location list is undefined so it's OK that we raise an exception. But for simple integration, the result is just zero. So, anything like this is wrong:

>>> solver.fields.reduction.area(locations=[])
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:\ANSYSDev\devZ3\vNNN\fluent\fluent25.1\cortex\pylib\flapi\services\reduction.py", line 37, in area
    return self._get_value(ctxt, "Area", locations)
  File "C:\ANSYSDev\devZ3\vNNN\commonfiles\CPython\3_10\winx64\Release\python\lib\contextlib.py", line 79, in inner
    return func(*args, **kwds)
  File "C:\ANSYSDev\devZ3\vNNN\fluent\fluent25.1\cortex\pylib\flapi\services\reduction.py", line 25, in _get_value
    locations = self._get_location_string(locations, ctxt)
  File "C:\ANSYSDev\devZ3\vNNN\commonfiles\CPython\3_10\winx64\Release\python\lib\site-packages\ansys\fluent\core\services\reduction.py", line 271, in _get_location_string
    return _locns(locations, ctxt)[0][1]
IndexError: list index out of range

Also, for averaging, we are not trapping this exception to escalate it to a higher-level, contextual exception - which we ought to do.