bug in atomic counter: read multi-versions data

某一次commit把原子计数器改坏了：
RowReader读时`SetMaxVersions()`设置多个版本，会读出原子计数器的多个内部版本。预期原子计数器只返回当前值。

例如：时间从t0 -> t2

```
t0:Add 3

t1:Put 5

t2:Add 8
```

预期：不论怎么设置，读出 13
现在：SetMaxVersions(2)，读出13和3

Start by tracing RowReader's handling of SetMaxVersions() for atomic-counter reads and inspect how internal versions are exposed. Reproduce the t0 Add 3, t1 Put 5, t2 Add 8 sequence with multiple version limits. Done means the reader returns only the current value, 13, regardless of the requested maximum versions.

Written by the indexing model from the issue text.