Error due to integer overflow being fixed in base julia

[pdeffebach]

There is a WIP PR here to fix some error with bounds checking in SkipMissing. When that is merged we should port the same fix to SkipMissings

[FedericoStra]

With the latest commit in the PR I'm trying to address this issue too.

As I mentioned in a comment in the PR, there is a small performance problem with _mapreduce for SkipMissing, which was already present. I haven't done anything to solve it in that regard.

[FedericoStra]

Ooops! I'm realizing now that this is an issue in another project 😅