Why Read next point if we're beyond the limit？

https://github.com/influxdata/influxdb/blob/5d84c602c8d68ef71c2e9bb11b5443d9822af67f/influxql/query/iterator.gen.go#L700

Hi, I test this continue will reduce performance.

I think we can do this ( i have tested, have a very good performance):
```go
// Next returns the next point from the iterator.
func (itr *floatLimitIterator) Next() (*FloatPoint, error) {
for {
if itr.opt.Limit > 0 && (itr.n-itr.opt.Offset) > itr.opt.Limit {Stuart Carnie, 1 year ago: • chore(tsdb): Initial commit of tsdb package
return nil, nil
}

p, err := itr.input.Next()
if p == nil || err != nil {
return nil, err
}
```

Start with influxql/query/iterator.gen.go around floatLimitIterator.Next at line 700, and trace how Limit, Offset, n, and input.Next interact. Reproduce the iterator behavior and compare the current and proposed stopping condition; done means preserving correct limit/offset results while addressing the reported unnecessary reads and performance impact.

Written by the indexing model from the issue text.