Improve error message when calling `unite` or `intersect`

[carlos-adir]

The functions unite and intersect call general_doer, but if any error happens it's hard to diagnose

src/shapepy/geometry/curve.py:661: in bezier_and_bezier
    left = rbool.unite(*tuple({p[0]} for p in pairs))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
../../.cache/pypoetry/virtualenvs/shapepy-ScE41tDE-py3.12/lib/python3.12/site-packages/rbool/bool1d.py:142: in unite
    return general_doer(subsets, or_func)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

subsets = (), function = <function unite.<locals>.or_func at 0x7d3e267fad40>

    def general_doer(
        subsets: Iterable[SubSetR1], function: Callable[[Real], bool]
    ) -> SubSetR1:
        """
        Receives a group of SubSetR1 and makes the union, the intersection,
        or the inversion depending on the given function.
    
        This is an internal function and should not be used careless
        """
        subsets = tuple(map(Future.convert, subsets))
        if not all(isinstance(subset, SubSetR1) for subset in subsets):
            raise TypeError
        set_all_knots: Set[Real] = set()
        for subset in subsets:
            set_all_knots |= set(extract_knots(subset))
        all_knots: List[Real] = sorted(set_all_knots)
        eval_knots: List[Real] = [0] * (2 * len(all_knots) + 1)
>       eval_knots[0] = all_knots[0] - 1
                        ^^^^^^^^^^^^
E       IndexError: list index out of range

../../.cache/pypoetry/virtualenvs/shapepy-ScE41tDE-py3.12/lib/python3.12/site-packages/rbool/bool1d.py:50: IndexError