## `tail()` silently returns empty result for negative `n` on sized iterables

When calling `tail()` with a negative `n` value on a sized iterable (like a string or list), no error is raised — it just returns an empty iterator. However, when the same negative `n` is passed with a non-sized iterator, a `ValueError` is raised.

This inconsistency makes the behavior of `tail(-1, ...)` depend on whether the iterable has a `__len__` method, which is surprising and hard to debug.

### Example

```python
import more_itertools as mi

# This raises ValueError as expected
try:
    list(mi.tail(-1, iter('ABCDEFG')))
except ValueError as e:
    print(f"Iterator raised: {e}")

# This silently returns [] instead of raising
result = list(mi.tail(-1, 'ABCDEFG'))
print(f"Sized iterable returned: {result}")  # prints []
```

Running the above, the non-sized iterator path raises `ValueError`, but the sized iterable path (`'ABCDEFG'` is a string with `__len__`) just returns an empty list with no error.

### Expected behavior

Passing a negative `n` to `tail()` should always raise a `ValueError`, regardless of whether the iterable is sized or not. Both `tail(-1, iter('ABCDEFG'))` and `tail(-1, 'ABCDEFG')` should raise `ValueError`.

### Actual behavior

`tail(-1, 'ABCDEFG')` returns an empty list `[]` silently instead of raising `ValueError`.

Work in `/workspace`. Submit your fix in the existing Python source files under `more_itertools`. Preserve the other public behavior. The environment is offline; dependencies are preinstalled. Grading runs the repository's test suite in a fresh environment, using your submitted source files.