Assertion `p_memberInit != __null' failed

@ppete is already working on this.

Since Jan 9, 2026.

Reproducer:
```cpp
typedef struct {
int foo;
} spinlock_t;

typedef struct wait_queue_head_t {
spinlock_t lock;
}wait_queue_head_t;

struct wait_queue_head_t work2 = {.lock = (spinlock_t ){(0)}};

void call_usermodehelper()
{
struct wait_queue_head_t work = {.lock = (spinlock_t ){(0)}};
work2;
}
```

```
Cxx_Grammar.C:275621: virtual SgType* SgDesignatedInitializer::get_type() const: Assertion `p_memberInit != __null' failed.
```