[clang] [clang][Static analyzer] fix crash on using `bitcast(<type>, <array>)` as array subscript (PR #101647)

[Balazs Benics via cfe-commits]

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@@ -472,7 +472,19 @@ SVal StoreManager::getLValueElement(QualType elementType, NonLoc Offset,
   const auto *ElemR = dyn_cast<ElementRegion>(BaseRegion);
 
   // Convert the offset to the appropriate size and signedness.
-  Offset = svalBuilder.convertToArrayIndex(Offset).castAs<NonLoc>();
+  auto Off = svalBuilder.convertToArrayIndex(Offset).getAs<NonLoc>();
+  if (!Off) {
+    // Handle cases when LazyCompoundVal is used for an array index.
+    // Such case is possible if code does:
+    //
+    //   char b[4];
+    //   a[__builtin_bitcast(int, b)];
+    //
----------------
steakhal wrote:

```suggestion
    //   char b[4];
    //   a[__builtin_bitcast(int, b)];
```

https://github.com/llvm/llvm-project/pull/101647