debug.c: Attempts to close stderr

https://github.com/jleffler/soq/blob/bb84e0704fb66a558fbcf507f43e76a7a547930e/src/libsoq/debug.c#L57C1-L59C1
```c
        if (debugfp != stdin && debugfp != stdout && debugfp != stderr)
            fclose(debugfp);
        debugfp = dbfp;
```

In `main`:
```c
    db_setfileptr(stderr);
```

Here, `debugfp` is initialized with 0 and then is attempted to close in `db_setfileptr`, leading to SEGFAULT