[WASM] `LowerAccessVectorElement` tries to cast `undef` to `ConstantSDNode` and crashes during casting

[DataCorrupted]

Reproduction: https://godbolt.org/z/PqK6Y1oa6

define <4 x float> @foo(i64 %i0, i64 %i1, ptr %p) {
  %B4 = urem i64 %i0, %i0
  %B5 = udiv i64 %i1, %B4
  %I = insertelement <4 x float> <float 0.25, float 0.25, float 0.25, float 0.25>, float 0.5, i64 %B5
  ret <4 x float>  %I
}

Cause:

In WebAssemblyISelLowering.cpp:2244, the UndefValue is also casted into ConstantSDNode, which causes the crash.

[llvmbot]

@llvm/issue-subscribers-backend-webassembly

[DataCorrupted]

Candidate patch: https://reviews.llvm.org/D147198