Tiering statistics have been broken for some time now, a regression
was introduced in 6f2406b0b6
Bonus fixes an issue where the objects are not assumed to be
of the 'STANDARD' storage-class for the objects that have
not yet tiered, this should be conditional based on the object's
metadata not a default assumption.
This PR also does some cleanup in terms of implementation,
fixes#18070
under some sequence of events following code would
reach an infinite loop.
```
idx1, idx2 := 0, 1
for ; idx2 != idx1; idx2++ {
fmt.Println(idx2)
}
```
fixes#15639
