When reading from file-like objects with the python client, we rely on fsspec to create an in-memory filesystem to store them.

The import cache is utilized for this, but a recent change that allows importing optional attributes/modules is causing problems here. Because the import silently fails, the object.ptr() is left as nullptr.
When the object's constructor is called, this causes a segfault.

I've fixed this here by checking if the object could not be imported before calling the constructor, but there are likely other places where this could become a problem.

In #7005 I've made changes to py::isinstance to support nullptr objects, maybe a better change would be to modify py::isinstance to take a PythonImportCacheItem object instead, and throw from the operator () of the item if it's called on an item that wasn't imported.

Also, I can't add a test for this, I've tried monkeypatching, but in the pyduckdb/filesystem.py we import fsspec, overriding the monkeypatch.