get_sample 返回的样本数比指定的窗口大小小1？

**Describe the bug (描述bug)**

照这样写法，假设 window_size 为7，get_sample 返回的样本数为 6，是否合理呢？

**To Reproduce (复现方法)**

**Expected behavior (期望行为)**
get_sample 返回的样本数与指定的窗口大小相等

**Versions (各种版本)**
OS:
Compiler:
brpc:
protobuf:

**Additional context/screenshots (更多上下文/截图)**

Start by locating the get_sample entry point in the C++ source and tracing how window_size determines the returned sample count. Reproduce the reported window_size of 7, then clarify whether the result should contain exactly seven samples and verify the behavior with a focused test.

Written by the indexing model from the issue text.