[clang] [analyzer] Do not attempt transition from sink node (PR #218970)

[Balázs Benics via cfe-commits]

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steakhal wrote:

I've just noticed this now that we have this `State == Pred->getState()` in the first `if` condition. Shouldn't we move the `if (!P) P = Pred;` part to the top to make that sound? What if `P` and `Pred` are different?

-- This doesn't have anything to do with your PR, but still related to some degree.

https://github.com/llvm/llvm-project/pull/218970