[clang] [Clang] Fix potential null pointer dereferences in Sema::AddInitializerToDecl (PR #94368)

[via cfe-commits]

smanna12 wrote:

```
if (Init && !Init->getType().isNull() &&
13716         !Init->getType()->isDependentType() && !VDeclType->isDependentType() &&
13717         Context.getAsIncompleteArrayType(VDeclType) &&
13718         Context.getAsIncompleteArrayType(Init->getType())) {
13719       // Bail out if it is not possible to deduce array size from the
13720       // initializer.
13721       Diag(VDecl->getLocation(), diag::err_typecheck_decl_incomplete_type)
13722           << VDeclType;
13723       VDecl->setInvalidDecl();
13724       return;
13725     }

```
Removing null check of ` Init ` would cause segfault for the test case`test/SemaCXX/paren-list-agg-init.cpp` when we try to access a member function (getType()) on a null pointer (Init)
```
int arr6[n](1, 2, 3); // expected-warning {{variable length arrays in C++ are a Clang extension}} \
                           expected-note {{function parameter 'n' with unknown value cannot be used in a constant expression}} \
                           expected-error {{variable-sized object may not be initialized}}

```

https://github.com/llvm/llvm-project/pull/94368