`need-check-nil` warning for `arr[#arr]` after length check

After checking the length of `arr`, emmylua will still report a `need-check-nil` warning when using `arr[#arr]`

### Example
```lua
---@class Foo
---@field bar number

---@type Foo[]
local arr = {}
if #arr > 0 then
    local v = arr[#arr].bar  -- Warning: arr[#arr] may be nil
end
```