[clang][analyzer] False positive core.NullDereference after updating list head through pointer-to-pointer backlink

**Description:**
The analyzer reports a null-pointer dereference on an impossible second loop iteration. The non-returning path in `reproducer()` expects a valid one-element list (`head -> [node] -> NULL`), and when updated inside `unlink_node()`, line `*node->previous = node->next;` is equivalent to `*(&head) = NULL`, so `head` becomes a `NULL` and the loop body execute only once.

**Reproducer:**
```c
#define NULL ((void*)0)

void clang_analyzer_eval(int);
void clang_analyzer_numTimesReached(void);

typedef struct Node Node;
struct Node {
Node *next;
Node **previous;
};

static Node *head;

void unlink_node(Node *node)
{
*node->previous = node->next;

if (node->next != NULL)
node->next->previous = node->previous;

node->previous = NULL;
node->next = NULL;
}

void reproducer(void)
{
if (head == NULL || head->next != NULL || head->previous != &head)
return;

clang_analyzer_eval(head->previous == &head);

while (head != 0) {
clang_analyzer_numTimesReached();

Node *node = head;
unlink_node(node);

clang_analyzer_eval(head == NULL);
}
}
```

**Output:**
```sh
mre.c:18:21: warning: Dereference of null pointer (loaded from field 'previous') [core.NullDereference]
18 | *node->previous = node->next;
| ~~~~~~~~ ^
mre.c:32:5: warning: UNKNOWN [debug.ExprInspection]
32 | clang_analyzer_eval(head->previous == &head);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mre.c:35:2: warning: 2 [debug.ExprInspection]
35 | clang_analyzer_numTimesReached();
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mre.c:40:2: warning: FALSE [debug.ExprInspection]
40 | clang_analyzer_eval(head == NULL);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
However, the analyzer:
- reports UNKNOWN for `head->previous == &head` (should be TRUE);
- reports FALSE for `head == NULL` after unlinking (should be TRUE);
- reaches the loop body twice (should be only once);
- reports a null dereference during the second iteration.

**Clang version:**
```sh
clang version 24.0.0git (https://github.com/llvm/llvm-project.git d71427f70210606cc41a460b4a1101b99e5f882f)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Build config: +assertions
```

Start by running the supplied reproducer() with the stated Clang version and compare the analyzer output with the expected pointer updates. Trace unlink_node(), especially the pointer-to-pointer assignment and the calls to clang_analyzer_eval() and clang_analyzer_numTimesReached(); done means the assertions report TRUE, the loop reaches once, and no null-dereference warning is emitted.

Written by the indexing model from the issue text.