replace the first iterator with the first valid iterator in First()

Could you describe the problem, current behaviour and expected behaviour?

This should look like this:

Problem

The it.First() returns false when first selector in SelectorPoints / SelectorRanges does not contain any rows even though the next point selectors have valid rows.

The it.Last() returns false when the last selector in SelectorPoints / SelectorRanges does not contain any rows even though the prev selectors have valid rows.

Behaviour

The iteration is over prematurely resulting in not iterating through all selected rows.

Expected Behaviour

All rows selected are iterated.

go-bond / bond

replace the first iterator with the first valid iterator in First() #120

Problem

Behaviour

Expected Behaviour