Catch invalid metric output

[leanderweber]

Description of the problem

Some metrics may output inf or nan values when inputting certain attributions.

Description of a solution

Such behavior should be caught and, at the very least, the user should be warned that the output contains invalid values and may need to be sorted out. Optimally, some information about what caused this could be given. E.g., 0 attributions, nan attributions were passed etc?

Minimum acceptance criteria

• Above warning is implemented.
• No metric "quietly" outputs invalid values anymore.
• @annahedstroem