Bvar return true not false when failed to read stat

**Describe the bug**
Bvar return -1 not false when failed to read stat

```
if (butil::read_command_output(oss, cmdbuf) != 0) {
        LOG(ERROR) << "Fail to read memory state";
        return -1;
    }
```

**To Reproduce**


**Expected behavior**
Bvar return  false when failed to read stat


**Versions**
OS:
Compiler:
brpc:
protobuf:

**Additional context/screenshots**

