[clang] [Clang] Prevent potential null pointer dereferences (PR #117176)

[Steven Perron via cfe-commits]

================
@@ -1908,9 +1908,9 @@ bool SemaHLSL::CheckBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall) {
       return true;
     // ensure both args have 3 elements
     int NumElementsArg1 =
-        TheCall->getArg(0)->getType()->getAs<VectorType>()->getNumElements();
+        TheCall->getArg(0)->getType()->casAs<VectorType>()->getNumElements();
----------------
s-perron wrote:

```suggestion
        TheCall->getArg(0)->getType()->castAs<VectorType>()->getNumElements();
```

https://github.com/llvm/llvm-project/pull/117176