fix: occur infinity-loop when include @FocusState

[YusukeHosonuma]

Occur infinity-loop in pretty-print when include @FocusState in target.
This PR is a temporary fix to prevent this issue.

//
// prettyPrint()
//
ContentView(
    email: "xxx@example.com",
    password: "pass",
    focus: <can not lookup>
)

//
// prettyPrintDebug()
//
ContentView(
    email: @State("xxx@example.com"),
    password: @State("pass"),
    focus: @FocusState(<can not lookup>)
)

[sahara-ooga]

LGTM!

I hope we'll find fundamental solution in the near future.. :-)
I described the desire in the issue #183.

[YusukeHosonuma]

Thanks for review!