[llvm] [GlobalISel] Fix UMR in `SwiftErrorValueTracking` (PR #190273)

[Yuta Saito via llvm-commits]

kateinoigakukun wrote:

@QuantumSegfault Oh, good point. `setCurrentVReg(..., nullptr, ...)` shouldn't be problematic immediately but better to align with SelectionDAG by adding `supportSwiftError` checks.

https://github.com/llvm/llvm-project/pull/190273