Defining optional globals doesn't trigger nil check warning

还没有人认领这个 Issue。

### How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

Windows

### What is the issue affecting?

Type Checking

### Expected Behaviour

I have some code that runs in different environments that have different global variables available.

For example, environment1 may have a global table C_GameRules available with a function in it. environment2 does not have the global available.

I'm trying to write a meta file that makes this optional nature of this global available:

```
---@meta

---@type table?
C_GameRules = nil

---@return boolean
function C_GameRules.IsHardcoreActive() end
```

I've also tried to define a class, no change in behavior

### Actual Behaviour

`C_GameRules.IsHardcoreActive()` does not trigger a need-nil-check warning, but the type of C_GameRules gets shown as `table?`

### Reproduction steps

see above

### Additional Notes

i don't want the inner field as nilable, environment 1 has "C_GameRules" as global available and the function is guaranteed to be in there, environment 2 has the global set to nil

### Log File

_No response_

使用所示的 Lua 元文件声明在 Visual Studio Code Extension 中复现该报告，并检查 C_GameRules.IsHardcoreActive() 的类型检查诊断。当可选全局变量产生 nil 检查警告，而其内部函数仍保持不可为 nil 时，即表示完成。

由索引模型根据 Issue 内容生成。