Typo and potential null dereference in HLMatrixBitcastLowerPass.cpp

[adam-yang]

https://github.com/microsoft/DirectXShaderCompiler/blob/8f2881e51178346547c2bf58c74691e05c5cf825/lib/HLSL/HLMatrixBitcastLowerPass.cpp#L229C28-L229C32

The LI below should be ST. The LI is from the previous if testing for U's type.

    } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
    ...
    } else if (StoreInst *ST = dyn_cast<StoreInst>(U)) {
      Value *V = ST->getValueOperand();
      if (VectorType *Ty = dyn_cast<VectorType>(V->getType())) {
        IRBuilder<> Builder(LI); // <---- Should be `ST`
        Value *zeroIdx = Builder.getInt32(0);
        unsigned vecSize = Ty->getNumElements();
        for (unsigned i = 0; i < vecSize; i++) {
          Value *GEP = CreateEltGEP(A, i, zeroIdx, Builder);
          Value *Elt = Builder.CreateExtractElement(V, i);
          Builder.CreateStore(Elt, GEP);
        }
        ST->eraseFromParent();

I made an issue instead of a PR because I don't have a test case, just noticed this typo.

[pow2clk]

Another side-effect of ms-extensions. They were added for the UUID implementation: see #5186