Fix PositiveInfinityResultNode returns positive infinity

[johansolbakken]

• grouping_adv system tests worked.

@arnej27959 please review

[arnej27959]

The new code
std::numeric_limits<int64_t>::infinity()
doesn't really do what one would guess, so either keep it as 0
or consider using max() instead.
Also, I think we can use the "new" way to ignore the index parameter here.
My suggested change may break some unit test, please check if you want to use it.