[clang][Interp] Fix null Descriptor dereference in ArrayElemPtrPop

ByteCode interpretor could deref a null descriptor
when handling typeid (or function pointers) in
ArrayElemPtrPop. We need to treat this case as having no descriptor

Author: term-est

clang/lib/AST/ByteCode/Interp.h

@@ -3126,7 +3126,8 @@ inline bool ArrayElemPtrPop(InterpState &S, CodePtr OpPC) {
   }
 
   if (Offset.isZero()) {
-    if (Ptr.getFieldDesc()->isArray() && Ptr.getIndex() == 0) {
+    if (const Descriptor *Desc = Ptr.getFieldDesc();
+        Desc && Desc->isArray() && Ptr.getIndex() == 0) {
       S.Stk.push<Pointer>(Ptr.atIndex(0).narrow());
       return true;
     }