flow: if (0) {... }

We need to ignore impossible paths, otherwise we have some errors like warning 33: dereference a NULL object

```c
#pragma safety enable

int main()
{
    int * _Opt p = 0;
    if (p)
    {
       *p = 1;
    }
}

```

```
main.c:6:9: warning 28: pointer is always null
 6 |    if (p)
   |        ~  
main.c:8:9: warning 33: dereference a NULL object
 8 |       *p = 1;
   |        ~      
```
