Detect 0 raised to negative exponents

[alexmo1997]

For 0^-1, numbat gives inf as a result. However, 0^-1 should be equally undefined just as 1/0.

[sharkdp]

Yes, thank you for reporting this. I think we should probably catch this, but in general, we won't be able to turn all calculations that potentially return inf into runtime errors. Numbat is a numerical calculator and can not analytically determine in all cases if a calculations will result in inf/NaN.