dt.insert() with empty array crashes at rust level if `insertionstrategy="BBox"` is used

[hugoledoux]

import startinpy
ls = []
dt = startinpy.DT()
dt.insert(ls, insertionstrategy="BBox")
print(dt)

==>

thread '<unnamed>' panicked at /Users/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/startin-0.8.2/src/lib.rs:1337:59:
called `Option::unwrap()` on a `None` value
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
  File "/Users/hugo/temp/rr.py", line 9, in <module>
    dt.insert(ls, insertionstrategy="BBox")
pyo3_runtime.PanicException: called `Option::unwrap()` on a `None` value