[clang] [clang][analyzer] Correct SMT Layer for _BitInt cases refutations (PR #143310)

[Balazs Benics via cfe-commits]

================
@@ -570,23 +572,37 @@ class SMTConv {
   // TODO: Refactor to put elsewhere
   static inline QualType getAPSIntType(ASTContext &Ctx,
                                        const llvm::APSInt &Int) {
-    return Ctx.getIntTypeForBitwidth(Int.getBitWidth(), Int.isSigned());
+    QualType Ty = Ctx.getIntTypeForBitwidth(Int.getBitWidth(), Int.isSigned());
----------------
steakhal wrote:

```suggestion
    if (QualType Ty = Ctx.getIntTypeForBitwidth(Int.getBitWidth(), Int.isSigned()); !Ty.isNull())
      return Ty;
```

Then deindent the rest of the code and drop the isNull check.

https://github.com/llvm/llvm-project/pull/143310